In vitro determination of analyte levels within body fluids

ABSTRACT

A reagentless whole-blood analyte detection system that is capable of being deployed near a patient has a source capable of emitting a beam of radiation that includes a spectral band. The whole-blood system also has a detector in an optical path of the beam. The whole-blood system also has a housing that is configured to house the source and the detector. The whole-blood system also has a sample element that is situated in the optical path of the beam. The sample element has a sample cell and a sample cell wall that does not eliminate transmittance of the beam of radiation in the spectral band.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/007,502, filed Jan. 14, 2011, now U.S. Pat. No. 7,999,927, which is acontinuation of U.S. application Ser. No. 12/815,372, filed Jun. 14,2010, now U.S. Pat. No. 7,872,734, which is a continuation of U.S.application Ser. No. 12/343,218, filed Dec. 23, 2008, now U.S. Pat. No.7,738,085, which is a continuation of U.S. application Ser. No.11/337,943, filed Jan. 23, 2006, now U.S. Pat. No. 7,480,032, which iscontinuation of U.S. application Ser. No. 10/219,625, filed Aug. 14,2002, now U.S. Pat. No. 6,989,891, which is a continuation-in-part ofU.S. application Ser. No. 10/055,875, filed Jan. 21, 2002, now U.S. Pat.No. 6,958,809, which claims the benefit of U.S. Provisional ApplicationNo. 60/340,794, filed Dec. 11, 2001, and of U.S. Provisional ApplicationNo. 60/346,383, filed Nov. 8, 2001. The entire contents of each of theabove-referenced patent applications and patents are incorporated byreference herein and made a part of this specification.

BACKGROUND

1. Field

This invention relates generally to determining analyte concentrationsin material samples.

2. Description of Related Art

Millions of diabetics draw samples of bodily fluid such as blood on adaily basis to monitor the level of glucose in their bloodstream. Thispractice is called self-monitoring, and is commonly performed using oneof a number of reagent-based glucose monitors. These monitors measureglucose concentration by observing some aspect of a chemical reactionbetween a reagent and the glucose in the fluid sample. The reagent is achemical compound that is known to react with glucose in a predictablemanner, enabling the monitor to determine the concentration of glucosein the sample. For example, the monitor may be configured to measure avoltage or a current generated by the reaction between the glucose andthe reagent. A small test strip is often employed to hold the reagentand to host the reaction between the glucose and the reagent.Reagent-based monitors and test strips suffer from a variety of problemsand also have limited performance.

Problems and costs relating to reagents arise during manufacture,shipment, storage, and use of the reagent-containing test strips. Costlyand demanding quality control strategies must be incorporated into thetest strip manufacturing processes to assure that the strips ultimatelyfunction properly. For example, a manufacturing lot-specific calibrationcode must be determined through blood or equivalent testing before thestrips can be released for consumer sale. The diabetics using thereagent-based monitors must often enter this calibration code into themonitor to ensure that the monitor accurately reads the concentration ofglucose in a sample placed on the strip. Naturally, this requirementleads to errors in reading and entering the calibration code, which cancause the monitor to make dangerously inaccurate readings of glucoseconcentration.

Reagent-based monitor test strips also require special packaging duringshipment and storage to prevent hydration of the reagent. Prematurehydration affects the manner in which the reagent reacts with glucoseand can cause erroneous readings. Once the test strips have beenshipped, they must be stored by the vendor and user within a controlledstorage temperature range. Unfortunately, the multitude of users areoften unable to follow these protocols. When test-strips and theirreagents are not properly handled and stored, erroneous monitor readingscan occur. Even when all necessary process, packaging, and storagecontrols are followed, the reagents on the strips still degrade withtime, and thus the strips have a limited shelf-life. All these factorshave led consumers to view reagent-based monitors and test strips asexpensive and troublesome. Indeed, reagent-based test strips would beeven more expensive if they were designed to be made simpler andcompletely fail-safe.

The performance of reagent-based glucose monitors is limited in a numberof respects related to reagents. As discussed above, the accuracy ofsuch monitors is limited by sensitive nature of the reagent, and thusany breakdown in the strict protocols relating to manufacture,packaging, storage, and use reduces the accuracy of the monitor. Thetime during which the reaction occurs between the glucose and thereagent is limited by the amount of reagent on the strip. Accordingly,the time for measuring the glucose concentration in the sample islimited as well. Confidence in the reagent-based blood glucose monitoroutput can be increased only be taking more fluid samples and makingadditional measurement. This is undesirable, because it doubles ortriples the numbers of painful fluid removals. At the same time,reagent-based monitor performance is limited in that the reaction ratelimits the speed with which an individual measurement can be obtained.The reaction time is regarded as too long by most users.

In general, reagent-based monitors are too complex for most users, andhave limited performance. In addition, such monitors require users todraw fluid multiple times per day using sharp lances, which must becarefully disposed of.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is a reagentless whole-bloodanalyte detection system that is capable of being deployed near apatient. The whole-blood system has a source capable of emitting a beamof radiation comprising a spectral band and a detector in an opticalpath of the beam. The whole-blood system also has a housing that isconfigured to house the source and the detector. The whole-blood systemalso has a sample element that is situated in the optical path of thebeam. The sample element has a sample cell and a sample cell wall thatdoes not eliminate transmittance of the beam of radiation in thespectral band.

In another embodiment, the present invention comprises a reagentlesswhole-blood analyte detection system. The whole-blood system has aradiation generating system that includes a radiation source and afilter that together generate electromagnetic radiation in at least onespectral band between about 4.2 μm and about 12.2 μm. The whole-bloodsystem also has an optical detector that is positioned in the opticalpath of the spectral band of radiation and that is responsive to thespectral band of radiation to generate a signal. The whole-blood systemalso has a signal processor that receives and processes the signal. Thesignal processor also generates an output. The whole-blood system alsohas a display and a sample extractor. A portable housing is configuredto house at least partially at least one of the radiation generatingsystem, the optical detector, the signal processor, and the sampleextractor. The housing is adapted to house a sample element that has atleast one optically transmissive portion.

In yet another embodiment, the present invention comprises a reagentlesswhole-blood analyte detection system. The whole-blood system has asource, an optical detector, and a sample element. The source isconfigured to emit electromagnetic radiation. The optical detector ispositioned in an optical path of the radiation. The sample element issituated in the optical path of the radiation. The whole-blood systemperforms optical analysis on a sample of whole-blood to assess at leastone characteristic of the whole-blood.

In another embodiment, a reagentless whole-blood analyte detectionsystem for analyzing a sample of whole-blood has an optical calibrationsystem and an optical analysis system. The optical calibration system isadapted to calibrate the whole-blood system at about the same time thatthe optical analysis system analyzes the sample of whole-blood.

In another embodiment, a method is provided for performing whole-bloodanalyte detection. A reagentless whole-blood analyte detection systemcapable of being deployed near a patient comprises an opticalcalibration system, an optical analysis system, and a sample cell isprovided. A substantial portion of the sample cell is filled with asample. A first calibration measurement of the sample cell is taken. Ananalytical measurement of a sample of whole-blood in the sample cell istaken.

In another embodiment, the present invention comprises a method forreagentless whole-blood analyte detection. A source, a detector in anoptical path of the source, a portable housing configured to house thesource and the detector, and a sample element that has a sample cell areprovided. A sample of fluid is drawn from a portion of tissue. Anopening of a sample element is positioned adjacent to the sample offluid so that the fluid is drawn into the sample element. The sampleelement is positioned in the housing so that the sample cell is in theoptical path of the source. An emitted radiation beam that comprises atleast one spectral band is emitted from the source to the sample cell ofthe sample element. A transmitted radiation beam comprising theradiation exiting the sample element is detected by the detector.

In another embodiment, the present invention comprises a method forreagentless whole-blood analyte detection that can be performed near apatient. A source configured to emit electromagnetic radiation and anoptical detector positioned in an optical path of the radiation areprovided. A portable housing that is configured to house at leastpartially the source and the optical detector and a sample element arealso provided. The sample element is situated in the housing in theoptical path of the radiation and contains a sample of whole-blood. Anemitted beam of electromagnetic radiation is emitted from the source. Atransmitted beam of radiation that is transmitted through the sample ofwhole-blood is detected to assess at least one characteristic of thesample of whole-blood.

In another embodiment, the present invention comprises a method foroperating a reagentless whole-blood detection system that is capable ofbeing deployed near a patient. The detection system has an opticalcalibration system and an optical analysis system. A sample elementcomprising a calibration portion and an analysis portion that has asample of whole-blood is advanced into the whole-blood analysis system.A first beam of electromagnetic radiation is transmitted through theanalysis portion of the sample element to determine an optical propertyof the sample of whole-blood and the sample element.

In another embodiment, an automatic reagentless whole-blood analytedetection system has a source, an optical detector, a sample extractor,a sample cell, and a signal processor. The source is capable ofgenerating radiation that includes at least wavelength ofelectromagnetic radiation. The optical detector is positioned in theoptical path of the radiation. The optical detector responds to theradiation by generating at least one signal. The sample extractor isconfigured to sample of fluid from a portion of tissue. The sample cellis situated in the optical path of the radiation and is configured toreceive the sample of fluid. The signal processor processes the signal.The testing system is configured to draw the sample of fluid, receivethe sample of fluid, to generate the radiation, to detect the radiation,and to process the signal without any intervention from the patient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a noninvasive optical detection system.

FIG. 2 is a perspective view of a window assembly for use with thenoninvasive detection system.

FIG. 3 is an exploded schematic view of an alternative window assemblyfor use with the noninvasive detection system.

FIG. 4 is a plan view of the window assembly connected to a coolingsystem.

FIG. 5 is a plan view of the window assembly connected to a coldreservoir.

FIG. 6 is a cutaway view of a heat sink for use with the noninvasivedetection system.

FIG. 6A is a cutaway perspective view of a lower portion of thenoninvasive detection system of FIG. 1.

FIG. 7 is a schematic view of a control system for use with thenoninvasive optical detection system.

FIG. 8 depicts a first methodology for determining the concentration ofan analyte of interest.

FIG. 9 depicts a second methodology for determining the concentration ofan analyte of interest.

FIG. 10 depicts a third methodology for determining the concentration ofan analyte of interest.

FIG. 11 depicts a fourth methodology for determining the concentrationof an analyte of interest.

FIG. 12 depicts a fifth methodology for determining the concentration ofan analyte of interest.

FIG. 13 is a schematic view of a reagentless whole-blood detectionsystem.

FIG. 14 is a perspective view of one embodiment of a cuvette for usewith the reagentless whole-blood detection system.

FIG. 15 is a plan view of another embodiment of a cuvette for use withthe reagentless whole-blood detection system.

FIG. 16 is a disassembled plan view of the cuvette shown in FIG. 15.

FIG. 16A is an exploded perspective view of the cuvette of FIG. 15.

FIG. 17 is a side view of the cuvette of FIG. 15.

FIG. 18 is a schematic view of a reagentless whole-blood detectionsystem having a communication port for connecting the system to otherdevices or networks.

FIG. 18A is a schematic view of a reagentless whole-blood detectionsystem having a noninvasive subsystem and a whole-blood subsystem.

FIG. 19 is a schematic view of a filter wheel incorporated into someembodiments of the whole-blood system of FIG. 13.

FIG. 20A is a top plan view of another embodiment of a whole-blood stripcuvette.

FIG. 20B is a side view of the whole-blood strip cuvette of FIG. 20A.

FIG. 20C is an exploded view of the embodiment of the whole-blood stripcuvette of FIG. 20A.

FIG. 21 is process flow chart illustrating a method for making anotherembodiment of a whole-blood strip cuvette.

FIG. 22 is a schematic illustration of a cuvette handler for packagingwhole-blood strip cuvettes made according to the process of FIG. 21 forthe system of FIG. 13.

FIG. 23A is a schematic illustration of a whole-blood strip cuvettehaving one type of flow enhancer.

FIG. 23B is a schematic illustration of a whole-blood strip cuvettehaving another type of flow enhancer.

FIG. 24A is a side view of a whole-blood strip cuvette with another typeof flow enhancer.

FIG. 24B is a cross sectional view of the whole-blood strip cuvette ofFIG. 24A showing the structure of one type of flow enhancer.

FIG. 25 is a schematic illustration of another embodiment of areagentless whole-blood detection system.

FIG. 26 is a schematic illustration of another embodiment of areagentless whole-blood detection system.

FIG. 27 is a schematic illustration of a cuvette configured forcalibration.

FIG. 28 is a plan view of one embodiment of a cuvette having anintegrated lance.

FIG. 28A is a plan view of another embodiment of a cuvette having anintegrated lance.

FIG. 29 is a plan view of another embodiment of a cuvette having anintegrated lance.

FIG. 30 is a graph of the measurement accuracy of the whole-bloodanalyte detection system versus measurement time.

FIG. 31 is a perspective view of another embodiment of a sample elementhaving an integrated lancing member.

FIG. 32 is a perspective view of a distal end of the sample element ofFIG. 31.

FIG. 32A is a cross-sectional view of the distal end of FIG. 32, takenalong line 32A-32A.

FIG. 32B is a cross-sectional view of the distal end of FIG. 32, takenalong line 32B-32B.

FIG. 32C is a cross-sectional view of a portion of the distal end ofFIG. 32B, illustrating an optical path through a chamber located in thedistal end.

FIG. 33 is an exploded perspective view of the sample element of FIG.31.

FIGS. 34A-34B are perspective views of another embodiment of a sampleelement having an integrated lancing member.

FIG. 35 is a perspective view of another embodiment of a sample elementhaving an integrated sample extractor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Although certain preferred embodiments and examples are disclosed below,it will be understood by those skilled in the art that the inventionextends beyond the specifically disclosed embodiments to otheralternative embodiments and/or uses of the invention and obviousmodifications and equivalents thereof. Thus, it is intended that thescope of the invention herein disclosed should not be limited by theparticular disclosed embodiments described below.

I. Overview of Analyte Detection Systems

Disclosed herein are analyte detection systems, including a noninvasivesystem discussed largely in part A below and a whole-blood systemdiscussed largely in part B below. Also disclosed are various methods,including methods for detecting the concentration of an analyte in amaterial sample. The noninvasive system/method and the whole-bloodsystem/method are related in that they both can employ opticalmeasurement. As used herein with reference to measurement apparatus andmethods, “optical” is a broad term and is used in its ordinary sense andrefers, without limitation, to identification of the presence orconcentration of an analyte in a material sample without requiring achemical reaction to take place. As discussed in more detail below, thetwo approaches each can operate independently to perform an opticalanalysis of a material sample. The two approaches can also be combinedin an apparatus, or the two approaches can be used together to performdifferent steps of a method.

In one embodiment, the two approaches are combined to performcalibration of an apparatus, e.g., of an apparatus that employs anoninvasive approach. In another embodiment, an advantageous combinationof the two approaches performs an invasive measurement to achievegreater accuracy and a whole-blood measurement to minimize discomfort tothe patient. For example, the whole-blood technique may be more accuratethan the noninvasive technique at certain times of the day, e.g., atcertain times after a meal has been consumed, or after a drug has beenadministered.

It should be understood, however, that any of the disclosed devices maybe operated in accordance with any suitable detection methodology, andthat any disclosed method may be employed in the operation of anysuitable device. Furthermore, the disclosed devices and methods areapplicable in a wide variety of situations or modes of operation,including but not limited to invasive, noninvasive, intermittent orcontinuous measurement, subcutaneous implantation, wearable detectionsystems, or any combination thereof.

Any method which is described and illustrated herein is not limited tothe exact sequence of acts described, nor is it necessarily limited tothe practice of all of the acts set forth. Other sequences of events oracts, or less than all of the events, or simultaneous occurrence of theevents, may be utilized in practicing the method(s) in question.

A. Noninvasive System

1. Monitor Structure

FIG. 1 depicts a noninvasive optical detection system (hereinafter“noninvasive system”) 10 in a presently preferred configuration. Thedepicted noninvasive system 10 is particularly suited for noninvasivelydetecting the concentration of an analyte in a material sample S, byobserving the infrared energy emitted by the sample, as will bediscussed in further detail below.

As used herein, the term “noninvasive” is a broad term and is used inits ordinary sense and refers, without limitation, to analyte detectiondevices and methods which have the capability to determine theconcentration of an analyte in in-vivo tissue samples or bodily fluids.It should be understood, however, that the noninvasive system 10disclosed herein is not limited to noninvasive use, as the noninvasivesystem 10 may be employed to analyze an in-vitro fluid or tissue samplewhich has been obtained invasively or noninvasively. As used herein, theterm “invasive” is a broad term and is used in its ordinary sense andrefers, without limitation, to analyte detection methods which involvethe removal of fluid samples through the skin. As used herein, the term“material sample” is a broad term and is used in its ordinary sense andrefers, without limitation, to any collection of material which issuitable for analysis by the noninvasive system 10. For example, thematerial sample S may comprise a tissue sample, such as a human forearm,placed against the noninvasive system 10. The material sample S may alsocomprise a volume of a bodily fluid, such as whole blood, bloodcomponent(s), interstitial fluid or intercellular fluid obtainedinvasively, or saliva or urine obtained noninvasively, or any collectionof organic or inorganic material. As used herein, the term “analyte” isa broad term and is used in its ordinary sense and refers, withoutlimitation, to any chemical species the presence or concentration ofwhich is sought in the material sample S by the noninvasive system 10.For example, the analyte(s) which may be detected by the noninvasivesystem 10 include but not are limited to glucose, ethanol, insulin,water, carbon dioxide, blood oxygen, cholesterol, bilirubin, ketones,fatty acids, lipoproteins, albumin, urea, creatinine, white blood cells,red blood cells, hemoglobin, oxygenated hemoglobin, carboxyhemoglobin,organic molecules, inorganic molecules, pharmaceuticals, cytochrome,various proteins and chromophores, microcalcifications, electrolytes,sodium, potassium, chloride, bicarbonate, and hormones. As used hereinto describe measurement techniques, the term “continuous” is a broadterm and is used in its ordinary sense and refers, without limitation,to the taking of discrete measurements more frequently than about onceevery 10 minutes, and/or the taking of a stream or series ofmeasurements or other data over any suitable time interval, for example,over an interval of one to several seconds, minutes, hours, days, orlonger. As used herein to describe measurement techniques, the term“intermittent” is a broad term and is used in its ordinary sense andrefers, without limitation, to the taking of measurements lessfrequently than about once every 10 minutes.

The noninvasive system 10 preferably comprises a window assembly 12,although in some embodiments the window assembly 12 may be omitted. Onefunction of the window assembly 12 is to permit infrared energy E toenter the noninvasive system 10 from the sample S when it is placedagainst an upper surface 12 a of the window assembly 12. The windowassembly 12 includes a heater layer (see discussion below) which isemployed to heat the material sample S and stimulate emission ofinfrared energy therefrom. A cooling system 14, preferably comprising aPeltier-type thermoelectric device, is in thermally conductive relationto the window assembly 12 so that the temperature of the window assembly12 and the material sample S can be manipulated in accordance with adetection methodology discussed in greater detail below. The coolingsystem 14 includes a cold surface 14 a which is in thermally conductiverelation to a cold reservoir 16 and the window assembly 12, and a hotsurface 14 b which is in thermally conductive relation to a heat sink18.

As the infrared energy E enters the noninvasive system 10, it firstpasses through the window assembly 12, then through an optical mixer 20,and then through a collimator 22. The optical mixer 20 preferablycomprises a light pipe having highly reflective inner surfaces whichrandomize the directionality of the infrared energy E as it passestherethrough and reflects against the mixer walls. The collimator 22also comprises a light pipe having highly-reflective inner walls, butthe walls diverge as they extend away from the mixer 20. The divergentwalls cause the infrared energy E to tend to straighten as it advancestoward the wider end of the collimator 22, due to the angle of incidenceof the infrared energy when reflecting against the collimator walls.

From the collimator 22 the infrared energy E passes through an array offilters 24, each of which allows only a selected wavelength or band ofwavelengths to pass therethrough. These wavelengths/bands are selectedto highlight or isolate the absorptive effects of the analyte ofinterest in the detection methodology discussed in greater detail below.Each filter 24 is preferably in optical communication with aconcentrator 26 and an infrared detector 28. The concentrators 26 havehighly reflective, converging inner walls which concentrate the infraredenergy as it advances toward the detectors 28, increasing the density ofthe energy incident upon the detectors 28.

The detectors 28 are in electrical communication with a control system30 which receives electrical signals from the detectors 28 and computesthe concentration of the analyte in the sample S. The control system 30is also in electrical communication with the window 12 and coolingsystem 14, so as to monitor the temperature of the window 12 and/orcooling system 14 and control the delivery of electrical power to thewindow 12 and cooling system 14.

a. Window Assembly

A preferred configuration of the window assembly 12 is shown inperspective, as viewed from its underside (in other words, the side ofthe window assembly 12 opposite the sample S), in FIG. 2. The windowassembly 12 generally comprises a main layer 32 formed of a highlyinfrared-transmissive material and a heater layer 34 affixed to theunderside of the main layer 32. The main layer 32 is preferably formedfrom diamond, most preferably from chemical-vapor-deposited (“CVD”)diamond, with a preferred thickness of about 0.25 millimeters. In otherembodiments alternative materials which are highlyinfrared-transmissive, such as silicon or germanium, may be used informing the main layer 32.

The heater layer 34 preferably comprises bus bars 36 located at opposingends of an array of heater elements 38. The bus bars 36 are inelectrical communication with the elements 38 so that, upon connectionof the bus bars 36 to a suitable electrical power source (not shown) acurrent may be passed through the elements 38 to generate heat in thewindow assembly 12. The heater layer 34 may also include one or moretemperature sensors (not shown), such as thermistors or resistancetemperature devices (RTDs), to measure the temperature of the windowassembly 12 and provide temperature feedback to the control system 30(see FIG. 1).

Still referring to FIG. 2, the heater layer 34 preferably comprises afirst adhesion layer of gold or platinum (hereinafter referred to as the“gold” layer) deposited over an alloy layer which is applied to the mainlayer 32. The alloy layer comprises a material suitable forimplementation of the heater layer 34, such as, by way of example, 10/90titanium/tungsten, titanium/platinum, nickel/chromium, or other similarmaterial. The gold layer preferably has a thickness of about 4000 .ANG.,and the alloy layer preferably has a thickness ranging between about 300. ANG. and about 500 .ANG.. The gold layer and/or the alloy layer may bedeposited onto the main layer 32 by chemical deposition including, butnot necessarily limited to, vapor deposition, liquid deposition,plating, laminating, casting, sintering, or other forming or depositionmethodologies well known to those or ordinary skill in the art. Ifdesired, the heater layer 34 may be covered with an electricallyinsulating coating which also enhances adhesion to the main layer 32.One preferred coating material is aluminum oxide. Other acceptablematerials include, but are not limited to, titanium dioxide or zincselenide.

The heater layer 34 may incorporate a variable pitch distance betweencenterlines of adjacent heater elements 38 to maintain a constant powerdensity, and promote a uniform temperature, across the entire layer 34.Where a constant pitch distance is employed, the preferred distance isat least about 50-100 microns. Although the heater elements 38 generallyhave a preferred width of about 25 microns, their width may also bevaried as needed for the same reasons stated above.

Alternative structures suitable for use as the heater layer 34 include,but are not limited to, thermoelectric heaters, radiofrequency (RF)heaters, infrared radiation heaters, optical heaters, heat exchangers,electrical resistance heating grids, wire bridge heating grids, or laserheaters. Whichever type of heater layer is employed, it is preferredthat the heater layer obscures about 10% or less of the window assembly12.

In a preferred embodiment, the window assembly 12 comprisessubstantially only the main layer 32 and the heater layer 34. Thus, wheninstalled in an optical detection system such as the noninvasive system10 shown in FIG. 1, the window assembly 12 will facilitate a minimallyobstructed optical path between a (preferably flat) upper surface 12 aof the window assembly 12 and the infrared detectors 28 of thenoninvasive system 10. The optical path 32 in the preferred noninvasivesystem 10 proceeds only through the main layer 32 and heater layer 34 ofthe window assembly 12 (including any antireflective, index-matching,electrical insulating or protective coatings applied thereto or placedtherein), through the optical mixer 20 and collimator 22 and to thedetectors 28.

FIG. 3 depicts an exploded side view of an alternative configuration forthe window assembly 12, which may be used in place of the configurationshown in FIG. 2. The window assembly 12 depicted in FIG. 3 includes nearits upper surface (the surface intended for contact with the sample S) ahighly infrared-transmissive, thermally conductive spreader layer 42.Underlying the spreader layer 42 is a heater layer 44. A thinelectrically insulating layer (not shown), such as layer of aluminumoxide, titanium dioxide or zinc selenide, may be disposed between theheater layer 44 and the spreader layer 42. (An aluminum oxide layer alsoincreases adhesion of the heater layer 44 to the spreader layer 42.)Adjacent to the heater layer 44 is a thermal insulating and impedancematching layer 46. Adjacent to the thermal insulating layer 46 is athermally conductive inner layer 48. The spreader layer 42 is coated onits top surface with a thin layer of protective coating 50. The bottomsurface of the inner layer 48 is coated with a thin overcoat layer 52.Preferably, the protective coating 50 and the overcoat layer 52 haveantireflective properties.

The spreader layer 42 is preferably formed of a highlyinfrared-transmissive material having a high thermal conductivitysufficient to facilitate heat transfer from the heater layer 44uniformly into the material sample S when it is placed against thewindow assembly 12. Other effective materials include, but are notlimited to, CVD diamond, diamondlike carbon, gallium arsenide,germanium, and other infrared-transmissive materials having sufficientlyhigh thermal conductivity. Preferred dimensions for the spreader layer42 are about one inch in diameter and about 0.010 inch thick. As shownin FIG. 3, a preferred embodiment of the spreader layer 42 incorporatesa beveled edge. Although not required, an approximate 45-degree bevel ispreferred.

The protective layer 50 is intended to protect the top surface of thespreader layer 42 from damage. Ideally, the protective layer is highlyinfrared-transmissive and highly resistant to mechanical damage, such asscratching or abrasion. It is also preferred that the protective layer50 and the overcoat layer 52 have high thermal conductivity andantireflective and/or index-matching properties. A satisfactory materialfor use as the protective layer 50 and the overcoat layer 52 is themulti-layer Broad Band Anti-Reflective Coating produced by DepositionResearch Laboratories, Inc. of St. Charles, Mo. Diamondlike carboncoatings are also suitable.

Except as noted below, the heater layer 44 is generally similar to theheater layer 34 employed in the window assembly shown in FIG. 2.Alternatively, the heater layer 44 may comprise a dopedinfrared-transmissive material, such as a doped silicon layer, withregions of higher and lower resistivity. The heater layer 44 preferablyhas a resistance of about 2 ohms and has a preferred thickness of about1,500 angstroms. A preferred material for forming the heater layer 44 isa gold alloy, but other acceptable materials include, but are notlimited to, platinum, titanium, tungsten, copper, and nickel.

The thermal insulating layer 46 prevents the dissipation of heat fromthe heater element 44 while allowing the cooling system 14 toeffectively cool the material sample S (see FIG. 1). This layer 46comprises a material having thermally insulative (e.g., lower thermalconductivity than the spreader layer 42) and infrared transmissivequalities. A preferred material is a germanium-arsenic-selenium compoundof the calcogenide glass family known as AMTIR-1 produced by AmorphousMaterials, Inc. of Garland, Tex. The pictured embodiment has a diameterof about 0.85 inches and a preferred thickness in the range of about0.005 to about 0.010 inches. As heat generated by the heater layer 44passes through the spreader layer 42 into the material sample S, thethermal insulating layer 46 insulates this heat.

The inner layer 48 is formed of thermally conductive material,preferably crystalline silicon formed using a conventional floatzonecrystal growth method. The purpose of the inner layer 48 is to serve asa cold-conducting mechanical base for the entire layered windowassembly.

The overall optical transmission of the window assembly 12 shown in FIG.3 is preferably at least 70%. The window assembly 12 of FIG. 3 ispreferably held together and secured to the noninvasive system 10 by aholding bracket (not shown). The bracket is preferably formed of aglass-filled plastic, for example Ultem 2300, manufactured by GeneralElectric. Ultem 2300 has low thermal conductivity which prevents heattransfer from the layered window assembly 12.

b. Cooling System

The cooling system 14 (see FIG. 1) preferably comprises a Peltier-typethermoelectric device. Thus, the application of an electrical current tothe preferred cooling system 14 causes the cold surface 14 a to cool andcauses the opposing hot surface 14 b to heat up. The cooling system 14cools the window assembly 12 via the situation of the window assembly 12in thermally conductive relation to the cold surface 14 a of the coolingsystem 14. It is contemplated that the cooling system 14, the heaterlayer 34, or both, can be operated to induce a desired time-varyingtemperature in the window assembly 12 to create an oscillating thermalgradient in the sample S, in accordance with various analyte-detectionmethodologies discussed herein.

Preferably, the cold reservoir 16 is positioned between the coolingsystem 14 and the window assembly 12, and functions as a thermalconductor between the system 14 and the window assembly 12. The coldreservoir 16 is formed from a suitable thermally conductive material,preferably brass. Alternatively, the window assembly 12 can be situatedin direct contact with the cold surface 14 a of the cooling system 14.

In alternative embodiments, the cooling system 14 may comprise a heatexchanger through which a coolant, such as air, nitrogen or chilledwater, is pumped, or a passive conduction cooler such as a heat sink. Asa further alternative, a gas coolant such as nitrogen may be circulatedthrough the interior of the noninvasive system 10 so as to contact theunderside of the window assembly 12 (see FIG. 1) and conduct heattherefrom.

FIG. 4 is a top schematic view of a preferred arrangement of the windowassembly 12 (of the type shown in FIG. 2) and the cold reservoir 16, andFIG. 5 is a top schematic view of an alternative arrangement in whichthe window assembly 12 directly contacts the cooling system 14. The coldreservoir 16/cooling system 14 preferably contacts the underside of thewindow assembly 12 along opposing edges thereof, on either side of theheater layer 34. With thermal conductivity thus established between thewindow assembly 12 and the cooling system 14, the window assembly can becooled as needed during operation of the noninvasive system 10. In orderto promote a substantially uniform or isothermal temperature profileover the upper surface of the window assembly 12, the pitch distancebetween centerlines of adjacent heater elements 38 may be made smaller(thereby increasing the density of heater elements 38) near theregion(s) of contact between the window assembly 12 and the coldreservoir 16/cooling system 14. As a supplement or alternative, theheater elements 38 themselves may be made wider near these regions ofcontact. As used herein, “isothermal” is a broad term and is used in itsordinary sense and refers, without limitation, to a condition in which,at a given point in time, the temperature of the window assembly 12 orother structure is substantially uniform across a surface intended forplacement in thermally conductive relation to the material sample S.Thus, although the temperature of the structure or surface may fluctuateover time, at any given point in time the structure or surface maynonetheless be isothermal.

The heat sink 18 drains waste heat from the hot surface 14 b of thecooling system 16 and stabilizes the operational temperature of thenoninvasive system 10. The preferred heat sink 18 (see FIG. 6) comprisesa hollow structure formed from brass or any other suitable materialhaving a relatively high specific heat and high heat conductivity. Theheat sink 18 has a conduction surface 18 a which, when the heat sink 18is installed in the noninvasive system 18, is in thermally conductiverelation to the hot surface 14 b of the cooling system 14 (see FIG. 1).A cavity 54 is formed in the heat sink 18 and preferably contains aphase-change material (not shown) to increase the capacity of the sink18. A preferred phase change material is a hydrated salt, such ascalcium chloride hexahydrate, available under the name TH29 from PCMThermal Solutions, Inc., of Naperville, Ill. Alternatively, the cavity54 may be omitted to create a heat sink 18 comprising a solid, unitarymass. The heat sink 18 also forms a number of fins 56 to furtherincrease the conduction of heat from the sink 18 to surrounding air.

Alternatively, the heat sink 18 may be formed integrally with theoptical mixer 20 and/or the collimator 22 as a unitary mass of rigid,heat-conductive material such as brass or aluminum. In such a heat sink,the mixer 20 and/or collimator 22 extend axially through the heat sink18, and the heat sink defines the inner walls of the mixer 20 and/orcollimator 22. These inner walls are coated and/or polished to haveappropriate reflectivity and nonabsorbance in infrared wavelengths aswill be further described below. Where such a unitary heatsink-mixer-collimator is employed, it is desirable to thermally insulatethe detector array from the heat sink.

It should be understood that any suitable structure may be employed toheat and/or cool the material sample S, instead of or in addition to thewindow assembly 12/cooling system 14 disclosed above, so long a properdegree of cycled heating and/or cooling are imparted to the materialsample S. In addition other forms of energy, such as but not limited tolight, radiation, chemically induced heat, friction and vibration, maybe employed to heat the material sample S. It will be furtherappreciated that heating of the sample can achieved by any suitablemethod, such as convection, conduction, radiation, etc.

c. Optics

As shown in FIG. 1, the optical mixer 20 comprises a light pipe with aninner surface coating which is highly reflective and minimallyabsorptive in infrared wavelengths, preferably a polished gold coating,although other suitable coatings may be used where other wavelengths ofelectromagnetic radiation are employed. The pipe itself may befabricated from a another rigid material such as aluminum or stainlesssteel, as long as the inner surfaces are coated or otherwise treated tobe highly reflective. Preferably, the optical mixer 20 has a rectangularcross-section (as taken orthogonal to the longitudinal axis A-A of themixer 20 and the collimator 22), although other cross-sectional shapes,such as other polygonal shapes or circular or elliptical shapes, may beemployed in alternative embodiments. The inner walls of the opticalmixer 20 are substantially parallel to the longitudinal axis A-A of themixer 20 and the collimator 22. The highly reflective and substantiallyparallel inner walls of the mixer 20 maximize the number of times theinfrared energy E will be reflected between the walls of the mixer 20,thoroughly mixing the infrared energy E as it propagates through themixer 20. In a presently preferred embodiment, the mixer 20 is about 1.2inches to 2.4 inches in length and its cross-section is a rectangle ofabout 0.4 inches by about 0.6 inches. Of course, other dimensions may beemployed in constructing the mixer 20. In particular it is beadvantageous to miniaturize the mixer or otherwise make it as small aspossible.

Still referring to FIG. 1, the collimator 22 comprises a tube with aninner surface coating which is highly reflective and minimallyabsorptive in infrared wavelengths, preferably a polished gold coating.The tube itself may be fabricated from a another rigid material such asaluminum, nickel or stainless steel, as long as the inner surfaces arecoated or otherwise treated to be highly reflective. Preferably, thecollimator 22 has a rectangular cross-section, although othercross-sectional shapes, such as other polygonal shapes or circular,parabolic or elliptical shapes, may be employed in alternativeembodiments. The inner walls of the collimator 22 diverge as they extendaway from the mixer 20. Preferably, the inner walls of the collimator 22are substantially straight and form an angle of about 7 degrees withrespect to the longitudinal axis A-A. The collimator 22 aligns theinfrared energy E to propagate in a direction that is generally parallelto the longitudinal axis A-A of the mixer 20 and the collimator 22, sothat the infrared energy E will strike the surface of the filters 24 atan angle as close to 90 degrees as possible.

In a presently preferred embodiment, the collimator is about 7.5 inchesin length. At its narrow end 22 a, the cross-section of the collimator22 is a rectangle of about 0.4 inches by 0.6 inches. At its wide end 22b, the collimator 22 has a rectangular cross-section of about 1.8 inchesby 2.6 inches. Preferably, the collimator 22 aligns the infrared energyE to an angle of incidence (with respect to the longitudinal axis A-A)of about 0-15 degrees before the energy E impinges upon the filters 24.Of course, other dimensions or incidence angles may be employed inconstructing and operating the collimator 22.

With further reference to FIGS. 1 and 6A, each concentrator 26 comprisesa tapered surface oriented such that its wide end 26 a is adapted toreceive the infrared energy exiting the corresponding filter 24, andsuch that its narrow end 26 b is adjacent to the corresponding detector28. The inward-facing surfaces of the concentrators 26 have an innersurface coating which is highly reflective and minimally absorptive ininfrared wavelengths, preferably a polished gold coating. Theconcentrators 26 themselves may be fabricated from a another rigidmaterial such as aluminum, nickel or stainless steel, so long as theirinner surfaces are coated or otherwise treated to be highly reflective.

Preferably, the concentrators 26 have a rectangular cross-section (astaken orthogonal to the longitudinal axis A-A), although othercross-sectional shapes, such as other polygonal shapes or circular,parabolic or elliptical shapes, may be employed in alternativeembodiments. The inner walls of the concentrators converge as theyextend toward the narrow end 26 b. Preferably, the inner walls of thecollimators 26 are substantially straight and form an angle of about 8degrees with respect to the longitudinal axis A-A. Such a configurationis adapted to concentrate infrared energy as it passes through theconcentrators 26 from the wide end 26 a to the narrow end 26 b, beforereaching the detectors 28.

In a presently preferred embodiment, each concentrator 26 is about 1.5inches in length. At the wide end 26 a, the cross-section of eachconcentrator 26 is a rectangle of about 0.6 inches by 0.57 inches. Atthe narrow end 26 b, each concentrator 26 has a rectangularcross-section of about 0.177 inches by 0.177 inches. Of course, otherdimensions or incidence angles may be employed in constructing theconcentrators 26.

d. Filters

The filters 24 preferably comprise standard interference-type infraredfilters, widely available from manufacturers such as Optical CoatingLaboratory, Inc. (“OCLI”) of Santa Rosa, Calif. In the embodimentillustrated in FIG. 1, a 3.times.4 array of filters 24 is positionedabove a 3.times.4 array of detectors 28 and concentrators 26. Asemployed in this embodiment, the filters 24 are arranged in four groupsof three filters having the same wavelength sensitivity. These fourgroups have bandpass center wavelengths of 7.15 μm±0.03 μm, 8.40 μm±0.03μm, 9.48 μm±0.04 μm, and 11.10 μm±0.04 μm, respectively, whichcorrespond to wavelengths around which water and glucose absorbelectromagnetic radiation. Typical bandwidths for these filters rangefrom 0.20 μm to 0.50 μm.

In an alternative embodiment, the array of wavelength-specific filters24 may be replaced with a single Fabry-Perot interferometer, which canprovide wavelength sensitivity which varies as a sample of infraredenergy is taken from the material sample S. Thus, this embodimentpermits the use of only one detector 28, the output signal of whichvaries in wavelength specificity over time. The output signal can bede-multiplexed based on the wavelength sensitivities induced by theFabry-Perot interferometer, to provide a multiple-wavelength profile ofthe infrared energy emitted by the material sample S. In thisembodiment, the optical mixer 20 may be omitted, as only one detector 28need be employed.

In still other embodiments, the array of filters 24 may comprise afilter wheel that rotates different filters with varying wavelengthsensitivities over a single detector 24. Alternatively, anelectronically tunable infrared filter may be employed in a mannersimilar to the Fabry-Perot interferometer discussed above, to providewavelength sensitivity which varies during the detection process. Ineither of these embodiments, the optical mixer 20 may be omitted, asonly one detector 28 need be employed.

e. Detectors

The detectors 28 may comprise any detector type suitable for sensinginfrared energy, preferably in the mid-infrared wavelengths. Forexample, the detectors 28 may comprise mercury-cadmium-telluride (MCT)detectors. A detector such as a Fermionics (Simi Valley, Calif.) modelPV-9.1 with a PVA481-1 pre-amplifier is acceptable. Similar units fromother manufacturers such as Graseby (Tampa, Fla.) can be substituted.Other suitable components for use as the detectors 28 includepyroelectric detectors, thermopiles, bolometers, silicon microbolometersand lead-salt focal plane arrays.

f. Control System

FIG. 7 depicts the control system 30 in greater detail, as well as theinterconnections between the control system and other relevant portionsof the noninvasive system. The control system includes a temperaturecontrol subsystem and a data acquisition subsystem.

In the temperature control subsystem, temperature sensors (such as RTDsand/or thermistors) located in the window assembly 12 provide a windowtemperature signal to a synchronous analog-to-digital conversion system70 and an asynchronous analog-to-digital conversion system 72. The A/Dsystems 70, 72 in turn provide a digital window temperature signal to adigital signal processor (DSP) 74. The processor 74 executes a windowtemperature control algorithm and determines appropriate control inputsfor the heater layer 34 of the window assembly 12 and/or for the coolingsystem 14, based on the information contained in the window temperaturesignal. The processor 74 outputs one or more digital control signals toa digital-to-analog conversion system 76 which in turn provides one ormore analog control signals to current drivers 78. In response to thecontrol signal(s), the current drivers 78 regulate the power supplied tothe heater layer 34 and/or to the cooling system 14. In one embodiment,the processor 74 provides a control signal through a digital I/O device77 to a pulse-width modulator (PWM) control 80, which provides a signalthat controls the operation of the current drivers 78. Alternatively, alow-pass filter (not shown) at the output of the PWM provides forcontinuous operation of the current drivers 78.

In another embodiment, temperature sensors may be located at the coolingsystem 14 and appropriately connected to the A/D system(s) and processorto provide closed-loop control of the cooling system as well.

In yet another embodiment, a detector cooling system 82 is located inthermally conductive relation to one or more of the detectors 28. Thedetector cooling system 82 may comprise any of the devices disclosedabove as comprising the cooling system 14, and preferably comprises aPeltier-type thermoelectric device. The temperature control subsystemmay also include temperature sensors, such as RTDs and/or thermistors,located in or adjacent to the detector cooling system 82, and electricalconnections between these sensors and the asynchronous A/D system 72.The temperature sensors of the detector cooling system 82 providedetector temperature signals to the processor 74. In one embodiment, thedetector cooling system 82 operates independently of the windowtemperature control system, and the detector cooling system temperaturesignals are sampled using the asynchronous A/D system 72. In accordancewith the temperature control algorithm, the processor 74 determinesappropriate control inputs for the detector cooling system 82, based onthe information contained in the detector temperature signal. Theprocessor 74 outputs digital control signals to the D/A system 76 whichin turn provides analog control signals to the current drivers 78. Inresponse to the control signals, the current drivers 78 regulate thepower supplied to the detector cooling system 14. In one embodiment, theprocessor 74 also provides a control signal through the digital I/Odevice 77 and the PWM control 80, to control the operation of thedetector cooling system 82 by the current drivers 78. Alternatively, alow-pass filter (not shown) at the output of the PWM provides forcontinuous operation of the current drivers 78.

In the data acquisition subsystem, the detectors 28 respond to theinfrared energy E incident thereon by passing one or more analogdetector signals to a preamp 84. The preamp 84 amplifies the detectorsignals and passes them to the synchronous A/D system 70, which convertsthe detector signals to digital form and passes them to the processor74. The processor 74 determines the concentrations of the analyte(s) ofinterest, based on the detector signals and a concentration-analysisalgorithm and/or phase/concentration regression model stored in a memorymodule 88. The concentration-analysis algorithm and/orphase/concentration regression model may be developed according to anyof the analysis methodologies discussed herein. The processor maycommunicate the concentration results and/or other information to adisplay controller 86, which operates a display (not shown), such as anLCD display, to present the information to the user.

A watchdog timer 94 may be employed to ensure that the processor 74 isoperating correctly. If the watchdog timer 94 does not receive a signalfrom the processor 74 within a specified time, the watchdog timer 94resets the processor 74. The control system may also include a JTAGinterface 96 to enable testing of the noninvasive system 10.

In one embodiment, the synchronous A/D system 70 comprises a 20-bit, 14channel system, and the asynchronous A/D system 72 comprises a 16-bit,16 channel system. The preamp may comprise a 12-channel preampcorresponding to an array of 12 detectors 28.

The control system may also include a serial port 90 or otherconventional data port to permit connection to a personal computer 92.The personal computer can be employed to update the algorithm(s) and/orphase/concentration regression model(s) stored in the memory module 88,or to download a compilation of analyte-concentration data from thenoninvasive system. A real-time clock or other timing device may beaccessible by the processor 74 to make any time-dependent calculationswhich may be desirable to a user.

2. Analysis Methodology

The detector(s) 28 of the noninvasive system 10 are used to detect theinfrared energy emitted by the material sample S in various desiredwavelengths. At each measured wavelength, the material sample S emitsinfrared energy at an intensity which varies over time. The time-varyingintensities arise largely in response to the use of the window assembly12 (including its heater layer 34) and the cooling system 14 to induce athermal gradient in the material sample S. As used herein, “thermalgradient” is a broad term and is used in its ordinary sense and refers,without limitation, to a difference in temperature and/or thermal energybetween different locations, such as different depths, of a materialsample, which can be induced by any suitable method of increasing ordecreasing the temperature and/or thermal energy in one or morelocations of the sample. As will be discussed in detail below, theconcentration of an analyte of interest (such as glucose) in thematerial sample S can be determined with a device such as thenoninvasive system 10, by comparing the time-varying intensity profilesof the various measured wavelengths.

Analysis methodologies are discussed herein within the context ofdetecting the concentration of glucose within a material sample, such asa tissue sample, which includes a large proportion of water. However, itwill evident that these methodologies are not limited to this contextand may be applied to the detection of a wide variety of analytes withina wide variety of sample types. It should also be understood that othersuitable analysis methodologies and suitable variations of the disclosedmethodologies may be employed in operating an analyte detection system,such as the noninvasive system 10.

As shown in FIG. 8, a first reference signal P may be measured at afirst reference wavelength. The first reference signal P is measured ata wavelength where water strongly absorbs (e.g., 2.9 μm or 6.1 μm).Because water strongly absorbs radiation at these wavelengths, thedetector signal intensity is reduced at those wavelengths. Moreover, atthese wavelengths water absorbs the photon emissions emanating from deepinside the sample. The net effect is that a signal emitted at thesewavelengths from deep inside the sample is not easily detected. Thefirst reference signal P is thus a good indicator of thermal-gradienteffects near the sample surface and may be known as a surface referencesignal. This signal may be calibrated and normalized, in the absence ofheating or cooling applied to the sample, to a baseline value of 1. Forgreater accuracy, more than one first reference wavelength may bemeasured. For example, both 2.9 μm and 6.1 μm may be chosen as firstreference wavelengths.

As further shown in FIG. 8, a second reference signal R may also bemeasured. The second signal R may be measured at a wavelength wherewater has very low absorbance (e.g., 3.6 μm or 4.2 μm). This secondreference signal R thus provides the analyst with information concerningthe deeper regions of the sample, whereas the first signal P providesinformation concerning the sample surface. This signal may also becalibrated and normalized, in the absence of heating or cooling appliedto the sample, to a baseline value of 1. As with the first (surface)reference signal P, greater accuracy may be obtained by using more thanone second (deep) reference signal R.

In order to determine analyte concentration, a third (analytical) signalQ is also measured. This signal is measured at an IR absorbance peak ofthe selected analyte. The IR absorbance peaks for glucose are in therange of about 6.5 μm to 11.0 μm. This detector signal may also becalibrated and normalized, in the absence of heating or cooling appliedto the material sample S, to a baseline value of 1. As with thereference signals P, R, the analytical signal Q may be measured at morethan one absorbance peak.

Optionally, or additionally, reference signals may be measured atwavelengths that bracket the analyte absorbance peak. These signals maybe advantageously monitored at reference wavelengths which do notoverlap the analyte absorbance peaks. Further, it is advantageous tomeasure reference wavelengths at absorbance peaks which do not overlapthe absorbance peaks of other possible constituents contained in thesample.

a. Basic Thermal Gradient

As further shown in FIG. 8, the signal intensities P, Q, R are showninitially at the normalized baseline signal intensity of 1. This ofcourse reflects the baseline radiative behavior of a test sample in theabsence of applied heating or cooling. At a time t_(C), the surface ofthe sample is subjected to a temperature event which induces a thermalgradient in the sample. The gradient can be induced by heating orcooling the sample surface. The example shown in FIG. 8 uses cooling,for example, using a 10° C. cooling event. In response to the coolingevent, the intensities of the detector signals P, Q, R decrease overtime.

Since the cooling of the sample is neither uniform nor instantaneous,the surface cools before the deeper regions of the sample cool. As eachof the signals P, Q, R drop in intensity, a pattern emerges. Signalintensity declines as expected, but as the signals P, Q, R reach a givenamplitude value (or series of amplitude values: 150, 152, 154, 156,158), certain temporal effects are noted. After the cooling event isinduced at t_(C), the first (surface) reference signal P declines inamplitude most rapidly, reaching a checkpoint 150 first, at time t_(P).This is due to the fact that the first reference signal P mirrors thesample's radiative characteristics near the surface of the sample. Sincethe sample surface cools before the underlying regions, the surface(first) reference signal P drops in intensity first.

Simultaneously, the second reference signal R is monitored. Since thesecond reference signal R corresponds to the radiation characteristicsof deeper regions of the sample, which do not cool as rapidly as thesurface (due to the time needed for the surface cooling to propagateinto the deeper regions of the sample), the intensity of signal R doesnot decline until slightly later. Consequently, the signal R does notreach the magnitude 150 until some later time t_(R). In other words,there exists a time delay between the time t_(P) at which the amplitudeof the first reference signal P reaches the checkpoint 150 and the timet_(R) at which the second reference signal R reaches the same checkpoint150. This time delay can be expressed as a phase difference φ(λ).Additionally, a phase difference may be measured between the analyticalsignal Q and either or both reference signals P, R.

As the concentration of analyte increases, the amount of absorbance atthe analytical wavelength increases. This reduces the intensity of theanalytical signal Q in a concentration-dependent way. Consequently, theanalytical signal Q reaches intensity 150 at some intermediate timet_(Q). The higher the concentration of analyte, the more the analyticalsignal Q shifts to the left in FIG. 8. As a result, with increasinganalyte concentration, the phase difference φ(λ) decreases relative tothe first (surface) reference signal P and increases relative to thesecond (deep tissue) reference signal R. The phase difference(s) φ(λ)are directly related to analyte concentration and can be used to makeaccurate determinations of analyte concentration.

The phase difference φ(λ) between the first (surface) reference signal Pand the analytical signal Q is represented by the equation:φ(λ)=|t_(P)−t_(Q)| The magnitude of this phase difference decreases withincreasing analyte concentration.

The phase difference φ(λ) between the second (deep tissue) referencesignal R and the analytical signal Q signal is represented by theequation: φ(λ)=|t_(Q)−t_(R)| The magnitude of this phase differenceincreases with increasing analyte concentration.

Accuracy may be enhanced by choosing several checkpoints, for example,150, 152, 154, 156, and 158 and averaging the phase differences observedat each checkpoint. The accuracy of this method may be further enhancedby integrating the phase difference(s) continuously over the entire testperiod. Because in this example only a single temperature event (here, acooling event) has been induced, the sample reaches a new lowerequilibrium temperature and the signals stabilize at a new constantlevel I_(F). Of course, the method works equally well with thermalgradients induced by heating or by the application or introduction ofother forms of energy, such as but not limited to light, radiation,chemically induced heat, friction and vibration.

This methodology is not limited to the determination of phasedifference. At any given time (for example, at a time t_(X)) theamplitude of the analytical signal Q may be compared to the amplitude ofeither or both of the reference signals P, R. The difference inamplitude may be observed and processed to determine analyteconcentration.

This method, the variants disclosed herein, and the apparatus disclosedas suitable for application of the method(s), are not limited to thedetection of in-vivo glucose concentration. The method and disclosedvariants and apparatus may be used on human, animal, or even plantsubjects, or on organic or inorganic compositions in a non-medicalsetting. The method may be used to take measurements of in-vivo orin-vitro samples of virtually any kind. The method is useful formeasuring the concentration of a wide range of additional chemicalanalytes, including but not limited to, glucose, ethanol, insulin,water, carbon dioxide, blood oxygen, cholesterol, bilirubin, ketones,fatty acids, lipoproteins, albumin, urea, creatinine, white blood cells,red blood cells, hemoglobin, oxygenated hemoglobin, carboxyhemoglobin,organic molecules, inorganic molecules, pharmaceuticals, cytochrome,various proteins and chromophores, microcalcifications, hormones, aswell as other chemical compounds. To detect a given analyte, one needsonly to select appropriate analytical and reference wavelengths.

The method is adaptable and may be used to determine chemicalconcentrations in samples of body fluids (e.g., blood, urine or saliva)once they have been extracted from a patient. In fact, the method may beused for the measurement of in-vitro samples of virtually any kind.

b. Modulated Thermal Gradient

In a variation of the methodology described above, a periodicallymodulated thermal gradient can be employed to make accuratedeterminations of analyte concentration.

As previously shown in FIG. 8, once a thermal gradient is induced in thesample, the reference and analytical signals P, Q, R fall out of phasewith respect to each other. This phase difference φ(λ) is presentwhether the thermal gradient is induced through heating or cooling. Byalternatively subjecting the test sample to cyclic pattern of heating,cooling, or alternately heating and cooling, an oscillating thermalgradient may be induced in a sample for an extended period of time.

An oscillating thermal gradient is illustrated using a sinusoidallymodulated gradient. FIG. 9 depicts detector signals emanating from atest sample. As with the methodology shown in FIG. 8, one or morereference signals J, L are measured. One or more analytical signals Kare also monitored. These signals may be calibrated and normalized, inthe absence of heating or cooling applied to the sample, to a baselinevalue of 1. FIG. 9 shows the signals after normalization. At some timet_(C), a temperature event (e.g., cooling) is induced at the samplesurface. This causes a decline in the detector signal. As shown in FIG.8, the signals (P, Q, R) decline until the thermal gradient disappearsand a new equilibrium detector signal I_(F) is reached. In the methodshown in FIG. 9, as the gradient begins to disappear at a signalintensity 160, a heating event, at a time t_(W), is induced in thesample surface. As a result the detector output signals J, K, L willrise as the sample temperature rises. At some later time t_(C2), anothercooling event is induced, causing the temperature and detector signalsto decline. This cycle of cooling and heating may be repeated over atime interval of arbitrary length. Moreover, if the cooling and heatingevents are timed properly, a periodically modulated thermal gradient maybe induced in the test sample.

As previously explained in the discussions relating to FIG. 8, the phasedifference φ(λ) may be measured and used to determine analyteconcentration. FIG. 9 shows that the first (surface) reference signal Jdeclines and rises in intensity first. The second (deep tissue)reference signal L declines and rises in a time-delayed manner relativeto the first reference signal J. The analytical signal K exhibits atime/phase delay dependent on the analyte concentration. With increasingconcentration, the analytical signal K shifts to the left in FIG. 9. Aswith FIG. 8, the phase difference φ(λ) may be measured. For example, aphase difference φ(λ) between the second reference signal L and theanalytical signal K, may be measured at a set amplitude 162 as shown inFIG. 9. Again, the magnitude of the phase signal reflects the analyteconcentration of the sample.

The phase-difference information compiled by any of the methodologiesdisclosed herein can correlated by the control system 30 (see FIG. 1)with previously determined phase-difference information to determine theanalyte concentration in the sample. This correlation could involvecomparison of the phase-difference information received from analysis ofthe sample, with a data set containing the phase-difference profilesobserved from analysis of wide variety of standards of known analyteconcentration. In one embodiment, a phase/concentration curve orregression model is established by applying regression techniques to aset of phase-difference data observed in standards of known analyteconcentration. This curve is used to estimate the analyte concentrationin a sample based on the phase-difference information received from thesample.

Advantageously, the phase difference φ(λ) may be measured continuouslythroughout the test period. The phase-difference measurements may beintegrated over the entire test period for an extremely accurate measureof phase difference φ(λ). Accuracy may also be improved by using morethan one reference signal and/or more than one analytical signal.

As an alternative or as a supplement to measuring phase difference(s),differences in amplitude between the analytical and reference signal(s)may be measured and employed to determine analyte concentration.Additional details relating to this technique and not necessary torepeat here may be found in the Assignee's U.S. patent application Ser.No. 09/538,164, incorporated by reference below.

Additionally, these methods may be advantageously employed tosimultaneously measure the concentration of one or more analytes. Bychoosing reference and analyte wavelengths that do not overlap, phasedifferences can be simultaneously measured and processed to determineanalyte concentrations. Although FIG. 9 illustrates the method used inconjunction with a sinusoidally modulated thermal gradient, theprinciple applies to thermal gradients conforming to any periodicfunction. In more complex cases, analysis using signal processing withFourier transforms or other techniques allows accurate determinations ofphase difference φ(λ) and analyte concentration.

As shown in FIG. 10, the magnitude of the phase differences may bedetermined by measuring the time intervals between the amplitude peaks(or troughs) of the reference signals J, L and the analytical signal K.Alternatively, the time intervals between the “zero crossings” (thepoint at which the signal amplitude changes from positive to negative,or negative to positive) may be used to determine the phase differencebetween the analytical signal K and the reference signals J, L. Thisinformation is subsequently processed and a determination of analyteconcentration may then be made. This particular method has the advantageof not requiring normalized signals.

As a further alternative, two or more driving frequencies may beemployed to determine analyte concentrations at selected depths withinthe sample. A slow (e.g., 1 Hz) driving frequency creates a thermalgradient which penetrates deeper into the sample than the gradientcreated by a fast (e.g., 3 Hz) driving frequency. This is because theindividual heating and/or cooling events are longer in duration wherethe driving frequency is lower. Thus, the use of a slow drivingfrequency provides analyte-concentration information from a deeper“slice” of the sample than does the use of a fast driving frequency.

It has been found that when analyzing a sample of human skin, atemperature event of 10° C. creates a thermal gradient which penetratesto a depth of about 150 μm, after about 500 ms of exposure.Consequently, a cooling/heating cycle or driving frequency of 1 Hzprovides information to a depth of about 150 μm. It has also beendetermined that exposure to a temperature event of 10° C. for about 167ms creates a thermal gradient that penetrates to a depth of about 50 μm.Therefore, a cooling/heating cycle of 3 Hz provides information to adepth of about 50 μm. By subtracting the detector signal informationmeasured at a 3 Hz driving frequency from the detector signalinformation measured at a 1 Hz driving frequency, one can determine theanalyte concentration(s) in the region of skin between 50 and 150 μm. Ofcourse, a similar approach can be used to determine analyteconcentrations at any desired depth range within any suitable type ofsample.

As shown in FIG. 11, alternating deep and shallow thermal gradients maybe induced by alternating slow and fast driving frequencies. As with themethods described above, this variation also involves the detection andmeasurement of phase differences φ(λ) between reference signals G, G′and analytical signals H, H′. Phase differences are measured at bothfast (e.g., 3 Hz) and slow (e.g., 1 Hz) driving frequencies. The slowdriving frequency may continue for an arbitrarily chosen number ofcycles (in region SL₁), for example, two full cycles. Then the fastdriving frequency is employed for a selected duration, in region F₁. Thephase difference data is compiled in the same manner as disclosed above.In addition, the fast frequency (shallow sample) phase difference datamay be subtracted from the slow frequency (deep sample) data to providean accurate determination of analyte concentration in the region of thesample between the gradient penetration depth associated with the fastdriving frequency and that associated with the slow driving frequency.

The driving frequencies (e.g., 1 Hz and 3 Hz) can be multiplexed asshown in FIG. 12. The fast (3 Hz) and slow (1 Hz) driving frequenciescan be superimposed rather than sequentially implemented. Duringanalysis, the data can be separated by frequency (using Fouriertransform or other techniques) and independent measurements of phasedelay at each of the driving frequencies may be calculated. Onceresolved, the two sets of phase delay data are processed to determineabsorbance and analyte concentration.

Additional details not necessary to repeat here may be found in U.S.Pat. No. 6,198,949, titled SOLID-STATE NON-INVASIVE INFRARED ABSORPTIONSPECTROMETER FOR THE GENERATION AND CAPTURE OF THERMAL GRADIENT SPECTRAFROM LIVING TISSUE, issued Mar. 6, 2001; U.S. Pat. No. 6,161,028, titledMETHOD FOR DETERMINING ANALYTE CONCENTRATION USING PERIODIC TEMPERATUREMODULATION AND PHASE DETECTION, issued Dec. 12, 2000; U.S. Pat. No.5,877,500, titled MULTICHANNEL INFRARED DETECTOR WITH OPTICALCONCENTRATORS FOR EACH CHANNEL, issued on Mar. 2, 1999; U.S. patentapplication Ser. No. 09/538,164, filed Mar. 30, 2000 and titled METHODAND APPARATUS FOR DETERMINING ANALYTE CONCENTRATION USING PHASE ANDMAGNITUDE DETECTION OF A RADIATION TRANSFER FUNCTION; U.S. patentapplication Ser. No. 09/427,178 (published as WIPO PCT Publication No.WO 01/30236 on May 3, 2001), filed Oct. 25, 1999, titled SOLID-STATENON-INVASIVE THERMAL CYCLING SPECTROMETER; U.S. Provisional PatentApplication No. 60/336,404, filed Oct. 29, 2001, titled WINDOW ASSEMBLY;U.S. Provisional Patent Application No. 60/340,794, filed Dec. 11, 2001,titled REAGENT-LESS WHOLE-BLOOD GLUCOSE METER; U.S. Provisional PatentApplication No. 60/340,435, filed Dec. 12, 2001, titled CONTROL SYSTEMFOR BLOOD CONSTITUENT MONITOR; U.S. Provisional Patent Application No.60/340,654, filed Dec. 12, 2001, titled SYSTEM AND METHOD FOR CONDUCTINGAND DETECTING INFRARED RADIATION; U.S. Provisional Patent ApplicationNo. 60/340,773, filed Dec. 11, 2001, titled METHOD FOR TRANSFORMINGPHASE SPECTRA TO ABSORPTION SPECTRA; U.S. Provisional Patent ApplicationNo. 60/332,322, filed Nov. 21, 2001, titled METHOD FOR ADJUSTING SIGNALVARIATION OF AN ELECTRONICALLY CONTROLLED INFRARED TRANSMISSIVE WINDOW;U.S. Provisional Patent Application No. 60/332,093, filed Nov. 21, 2001,titled METHOD FOR IMPROVING THE ACCURACY OF AN ALTERNATE SITE BLOODGLUCOSE MEASUREMENT; U.S. Provisional Patent Application No. 60/332,125,filed Nov. 21, 2001, titled METHOD FOR ADJUSTING A BLOOD ANALYTEMEASUREMENT; U.S. Provisional Patent Application No. 60/341,435, filedDec. 14, 2001, titled PATH LENGTH-INDEPENDENT METHODS FOR OPTICALLYDETERMINING MATERIAL COMPOSITION; U.S. Provisional Patent ApplicationNo. 60/339,120, filed Dec. 7, 2001, titled QUADRATURE DEMODULATION ANDKALMAN FILTERING IN A BIOLOGICAL CONSTITUENT MONITOR; U.S. ProvisionalPatent Application No. 60/339,044, filed Nov. 12, 2001, titled FASTSIGNAL DEMODULATION WITH MODIFIED PHASE-LOCKED LOOP TECHNIQUES; U.S.Provisional Patent Application No. 60/336,294, filed Oct. 29, 2001,titled METHOD AND DEVICE FOR INCREASING ACCURACY OF BLOOD CONSTITUENTMEASUREMENT; U.S. Provisional Patent Application No. 60/338,992, filedNov. 13, 2001, titled SITE SELECTION FOR DETERMINING ANALYTECONCENTRATION IN LIVING TISSUE; and U.S. Provisional Patent ApplicationNo. 60/339,116, filed Nov. 7, 2001, titled METHOD AND APPARATUS FORIMPROVING CLINICALLY SIGNIFICANT ACCURACY OF ANALYTE MEASUREMENTS. Allof the above-mentioned patents, patent applications and publications arehereby incorporated by reference in their entirety herein and made apart of this specification.

B. Whole-Blood Detection System

FIG. 13 is a schematic view of a reagentless whole-blood analytedetection system 200 (hereinafter “whole-blood system”) in a preferredconfiguration. The whole-blood system 200 may comprise a radiationsource 220, a filter 230, a cuvette 240 that includes a sample cell 242,and a radiation detector 250. The whole-blood system 200 preferably alsocomprises a signal processor 260 and a display 270. Although a cuvette240 is shown here, other sample elements, as described below, could alsobe used in the system 200. The whole-blood system 200 can also comprisea sample extractor 280, which can be used to access bodily fluid from anappendage, such as the finger 290, forearm, or any other suitablelocation.

As used herein, the terms “whole-blood analyte detection system” and“whole-blood system” are broad, synonymous terms and are used in theirordinary sense and refer, without limitation, to analyte detectiondevices which can determine the concentration of an analyte in amaterial sample by passing electromagnetic radiation through the sampleand detecting the absorbance of the radiation by the sample. As usedherein, the term “whole-blood” is a broad term and is used in itsordinary sense and refers, without limitation, to blood that has beenwithdrawn from a patient but that has not been otherwise processed,e.g., it has not been hemolysed, lyophilized, centrifuged, or separatedin any other manner, after being removed from the patient. Whole-bloodmay contain amounts of other fluids, such as interstitial fluid orintracellular fluid, which may enter the sample during the withdrawalprocess or are naturally present in the blood. It should be understood,however, that the whole-blood system 200 disclosed herein is not limitedto analysis of whole-blood, as the whole-blood system 10 may be employedto analyze other substances, such as saliva, urine, sweat, interstitialfluid, intracellular fluid, hemolysed, lyophilized, or centrifuged bloodor any other organic or inorganic materials.

The whole-blood system 200 may comprise a near-patient testing system.As used herein, “near-patient testing system” is used in its ordinarysense and includes, without limitation, test systems that are configuredto be used where the patient is rather than exclusively in a laboratory,e.g., systems that can be used at a patient's home, in a clinic, in ahospital, or even in a mobile environment. Users of near-patient testingsystems can include patients, family members of patients, clinicians,nurses, or doctors. A “near-patient testing system” could also include a“point-of-care” system.

The whole-blood system 200 may in one embodiment be configured to beoperated easily by the patient or user. As such, the system 200 ispreferably a portable device. As used herein, “portable” is used in itsordinary sense and means, without limitation, that the system 200 can beeasily transported by the patient and used where convenient. Forexample, the system 200 is advantageously small. In one preferredembodiment, the system 200 is small enough to fit into a purse orbackpack. In another embodiment, the system 200 is small enough to fitinto a pants pocket. In still another embodiment, the system 200 issmall enough to be held in the palm of a hand of the user.

Some of the embodiments described herein employ a sample element to holda material sample, such as a sample of biological fluid. As used herein,“sample element” is a broad term and is used in its ordinary sense andincludes, without limitation, structures that have a sample cell and atleast one sample cell wall, but more generally includes any of a numberof structures that can hold, support or contain a material sample andthat allow electromagnetic radiation to pass through a sample held,supported or contained thereby; e.g., a cuvette, test strip, etc. Asused herein, the term “disposable” when applied to a component, such asa sample element, is a broad term and is used in its ordinary sense andmeans, without limitation, that the component in question is used afinite number of times and then discarded. Some disposable componentsare used only once and then discarded. Other disposable components areused more than once and then discarded.

The radiation source 220 of the whole-blood system 200 emitselectro-magnetic radiation in any of a number of spectral ranges, e.g.,within infrared wavelengths; in the mid-infrared wavelengths; aboveabout 0.8 μm; between about 5.0 μm and about 20.0 μm; and/or betweenabout 5.25 μm and about 12.0 μm. However, in other embodiments thewhole-blood system 200 may employ a radiation source 220 which emits inwavelengths found anywhere from the visible spectrum through themicrowave spectrum, for example anywhere from about 0.4 μm to greaterthan about 100 μm. In still further embodiments the radiation sourceemits electromagnetic radiation in wavelengths between about 3.5 μm andabout 14 μm, or between about 0.8 μm and about 2.5 μm, or between about2.5 μm and about 20 μm, or between about 20 μm and about 100 μm, orbetween about 6.85 μm and about 10.10 μm.

The radiation emitted from the source 220 is in one embodiment modulatedat a frequency between about one-half hertz and about one hundred hertz,in another embodiment between about 2.5 hertz and about 7.5 hertz, instill another embodiment at about 50 hertz, and in yet anotherembodiment at about 5 hertz. With a modulated radiation source, ambientlight sources, such as a flickering fluorescent lamp, can be more easilyidentified and rejected when analyzing the radiation incident on thedetector 250. One source that is suitable for this application isproduced by ION OPTICS, INC. and sold under the part number NL5LNC.

The filter 230 permits electromagnetic radiation of selected wavelengthsto pass through and impinge upon the cuvette/sample element 240.Preferably, the filter 230 permits radiation at least at about thefollowing wavelengths to pass through to the cuvette/sample element: 3.9μm, 4.0 μm, 4.05 μm, 4.2 μm, 4.75 μm, 4.95 μm, 5.25 μm, 6.12 μm, 7.4 μm,8.0 μm, 8.45 μm, 9.25 μm, 9.5 μm, 9.65 μm, 10.4 μm, 12.2 μm. In anotherembodiment, the filter 230 permits radiation at least at about thefollowing wavelengths to pass through to the cuvette/sample element:5.25 μm, 6.12 μm, 6.8 μm, 8.03 μm, 8.45 μm, 9.25 μm, 9.65 μm, 10.4 μm,12 μm. In still another embodiment, the filter 230 permits radiation atleast at about the following wavelengths to pass through to thecuvette/sample element: 6.85 μm, 6.97 μm, 7.39 μm, 8.23 μm, 8.62 μm,9.02 μm, 9.22 μm, 9.43 μm, 9.62 μm, and 10.10 μm. The sets ofwavelengths recited above correspond to specific embodiments within thescope of this disclosure. Furthermore, other subsets of the foregoingsets or other combinations of wavelengths can be selected. Finally,other sets of wavelengths can be selected within the scope of thisdisclosure based on cost of production, development time, availability,and other factors relating to cost, manufacturability, and time tomarket of the filters used to generate the selected wavelengths, and/orto reduce the total number of filters needed.

In one embodiment, the filter 230 is capable of cycling its passbandamong a variety of narrow spectral bands or a variety of selectedwavelengths. The filter 230 may thus comprise a solid-state tunableinfrared filter, such as that available from ION OPTICS INC. The filter230 could also be implemented as a filter wheel with a plurality offixed-passband filters mounted on the wheel, generally perpendicular tothe direction of the radiation emitted by the source 220. Rotation ofthe filter wheel alternately presents filters that pass radiation atwavelengths that vary in accordance with the filters as they passthrough the field of view of the detector 250.

The detector 250 preferably comprises a 3 mm long by 3 mm widepyroelectric detector. Suitable examples are produced by DIAS AngewandteSensorik GmbH of Dresden, Germany, or by BAE Systems (such as its TGSmodel detector). The detector 250 could alternatively comprise athermopile, a bolometer, a silicon microbolometer, a lead-salt focalplane array, or a mercury-cadmium-telluride (MCT) detector. Whicheverstructure is used as the detector 250, it is desirably configured torespond to the radiation incident upon its active surface 254 to produceelectrical signals that correspond to the incident radiation.

In one embodiment, the sample element comprises a cuvette 240 which inturn comprises a sample cell 242 configured to hold a sample of tissueand/or fluid (such as whole-blood, blood components, interstitial fluid,intercellular fluid, saliva, urine, sweat and/or other organic orinorganic materials) from a patient within its sample cell. The cuvette240 is installed in the whole-blood system 200 with the sample cell 242located at least partially in the optical path 243 between the radiationsource 220 and the detector 250. Thus, when radiation is emitted fromthe source 220 through the filter 230 and the sample cell 242 of thecuvette 240, the detector 250 detects the radiation signal strength atthe wavelength(s) of interest. Based on this signal strength, the signalprocessor 260 determines the degree to which the sample in the cell 242absorbs radiation at the detected wavelength(s). The concentration ofthe analyte of interest is then determined from the absorption data viaany suitable spectroscopic technique.

As shown in FIG. 13, the whole-blood system 200 can also comprise asample extractor 280. As used herein, the term “sample extractor” is abroad term and is used in its ordinary sense and refers, withoutlimitation, to or any device which is suitable for drawing a sample offluid from tissue, such as whole blood or other bodily fluids throughthe skin of a patient. In various embodiments, the sample extractor maycomprise a lance, laser lance, iontophoretic sampler, gas-jet, fluid-jetor particle-jet perforator, ultrasonic enhancer (used with or without achemical enhancer), or any other suitable device.

As shown in FIG. 13, the sample extractor 280 could form an opening inan appendage, such as the finger 290, to make whole-blood available tothe cuvette 240. It should be understood that other appendages could beused to draw the sample, including but not limited to the forearm. Withsome embodiments of the sample extractor 280, the user forms a tiny holeor slice through the skin, through which flows a sample of bodily fluidsuch as whole-blood. Where the sample extractor 280 comprises a lance(see FIG. 14), the sample extractor 280 may comprise a sharp cuttingimplement made of metal or other rigid materials. One suitable laserlance is the Lasette Plush.RTM. produced by Cell Robotics International,Inc. of Albuquerque, N. Mex. If a laser lance, iontophoretic sampler,gas-jet or fluid-jet perforator is used as the sample extractor 280, itcould be incorporated into the whole-blood system 200 (see FIG. 13), orit could be a separate device.

Additional information on laser lances can be found in U.S. Pat. No.5,908,416, issued Jun. 1, 1999, titled LASER DERMAL PERFORATOR; theentirety of this patent is hereby incorporated by reference herein andmade a part of this specification. One suitable gas-jet, fluid-jet orparticle-jet perforator is disclosed in U.S. Pat. No. 6,207,400, issuedMar. 27, 2001, titled NON- OR MINIMALLY INVASIVE MONITORING METHODSUSING PARTICLE DELIVERY METHODS; the entirety of this patent is herebyincorporated by reference herein and made a part of this specification.One suitable iontophoretic sampler is disclosed in U.S. Pat. No.6,298,254, issued Oct. 2, 2001, titled DEVICE FOR SAMPLING SUBSTANCESUSING ALTERNATING POLARITY OF IONTOPHORETIC CURRENT; the entirety ofthis patent is hereby incorporated by reference herein and made a partof this specification. One suitable ultrasonic enhancer, and chemicalenhancers suitable for use therewith, are disclosed in U.S. Pat. No.5,458,140, titled ENHANCEMENT OF TRANSDERMAL MONITORING APPLICATIONSWITH ULTRASOUND AND CHEMICAL ENHANCERS, issued Oct. 17, 1995, the entiredisclosure of which is hereby incorporated by reference and made a partof this specification.

FIG. 14 shows one embodiment of a sample element, in the form of acuvette 240, in greater detail. The cuvette 240 further comprises asample supply passage 248, a pierceable portion 249, a first window 244,and a second window 246, with the sample cell 242 extending between thewindows 244, 246. In one embodiment, the cuvette 240 does not have asecond window 246. The first window 244 (or second window 246) is oneform of a sample cell wall; in other embodiments of the sample elementsand cuvettes disclosed herein, any sample cell wall may be used that atleast partially contains, holds or supports a material sample, such as abiological fluid sample, and which is transmissive of at least somebands of electromagnetic radiation, and which may but need not betransmissive of electromagnetic radiation in the visible range. Thepierceable portion 249 is an area of the sample supply passage 248 thatcan be pierced by suitable embodiments of the sample extractor 280.Suitable embodiments of the sample extractor 280 can pierce the portion249 and the appendage 290 to create a wound in the appendage 290 and toprovide an inlet for the blood or other fluid from the wound to enterthe cuvette 240. (The sample extractor 280 is shown on the opposite sideof the sample element in FIG. 14, as compared to FIG. 13, as it maypierce the portion 249 from either side.)

The windows 244, 246 are preferably optically transmissive in the rangeof electromagnetic radiation that is emitted by the source 220, or thatis permitted to pass through the filter 230. In one embodiment, thematerial that makes up the windows 244, 246 is completely transmissive,i.e., it does not absorb any of the electromagnetic radiation from thesource 220 and filter 230 that is incident upon it. In anotherembodiment, the material of the windows 244, 246 has some absorption inthe electromagnetic range of interest, but its absorption is negligible.In yet another embodiment, the absorption of the material of the windows244, 246 is not negligible, but it is known and stable for a relativelylong period of time. In another embodiment, the absorption of thewindows 244, 246 is stable for only a relatively short period of time,but the whole-blood system 200 is configured to observe the absorptionof the material and eliminate it from the analyte measurement before thematerial properties can change measurably.

The windows 244, 246 are made of polypropylene in one embodiment. Inanother embodiment, the windows 244, 246 are made of polyethylene.Polyethylene and polypropylene are materials having particularlyadvantageous properties for handling and manufacturing, as is known inthe art. Also, polypropylene can be arranged in a number of structures,e.g., isotactic, atactic and syndiotactic, which may enhance the flowcharacteristics of the sample in the sample element. Preferably thewindows 244, 246 are made of durable and easily manufactureablematerials, such as the above-mentioned polypropylene or polyethylene, orsilicon or any other suitable material. The windows 244, 246 can be madeof any suitable polymer, which can be isotactic, atactic or syndiotacticin structure.

The distance between the windows 244, 246 comprises an opticalpathlength and can be between about 1 μm and about 100 μm. In oneembodiment, the optical pathlength is between about 10 μm and about 40μm, or between about 25 μm and about 60 μm, or between about 30 μm andabout 50 μm. In still another embodiment, the optical pathlength isabout 25 μm. The transverse size of each of the windows 244, 246 ispreferably about equal to the size of the detector 250. In oneembodiment, the windows are round with a diameter of about 3 mm. In thisembodiment, where the optical pathlength is about 25 μm the volume ofthe sample cell 242 is about 0.177 μL. In one embodiment, the length ofthe sample supply passage 248 is about 6 mm, the height of the samplesupply passage 248 is about 1 mm, and the thickness of the sample supplypassage 248 is about equal to the thickness of the sample cell, e.g., 25μm. The volume of the sample supply passage is about 0.150 μL. Thus, thetotal volume of the cuvette 240 in one embodiment is about 0.327 μL. Ofcourse, the volume of the cuvette 240/sample cell 242/etc. can vary,depending on many variables, such as the size and sensitivity of thedetectors 250, the intensity of the radiation emitted by the source 220,the expected flow properties of the sample, and whether flow enhancers(discussed below) are incorporated into the cuvette 240. The transportof fluid to the sample cell 242 is achieved preferably through capillaryaction, but may also be achieved through wicking, or a combination ofwicking and capillary action.

FIGS. 15-17 depict another embodiment of a cuvette 305 that could beused in connection with the whole-blood system 200. The cuvette 305comprises a sample cell 310, a sample supply passage 315, an air ventpassage 320, and a vent 325. As best seen in FIGS. 16, 16A and 17, thecuvette also comprises a first sample cell window 330 having an innerside 332, and a second sample cell window 335 having an inner side 337.As discussed above, the window(s) 330/335 in some embodiments alsocomprise sample cell wall(s). The cuvette 305 also comprises an opening317 at the end of the sample supply passage 315 opposite the sample cell310. The cuvette 305 is preferably about ¼-⅛ inch wide and about ¾ inchlong; however, other dimensions are possible while still achieving theadvantages of the cuvette 305.

The sample cell 310 is defined between the inner side 332 of the firstsample cell window 330 and the inner side 337 of the second sample cellwindow 335. The perpendicular distance T between the two inner sides332, 337 comprises an optical pathlength that can be between about 1 μmand about 1.22 mm. The optical pathlength can alternatively be betweenabout 1 μm and about 100 μm. The optical pathlength could stillalternatively be about 80 μm, but is preferably between about 10 μm andabout 50 μm. In another embodiment, the optical pathlength is about 25μm. The windows 330, 335 are preferably formed from any of the materialsdiscussed above as possessing sufficient radiation transmissivity. Thethickness of each window is preferably as small as possible withoutoverly weakening the sample cell 310 or cuvette 305.

Once a wound is made in the appendage 290, the opening 317 of the samplesupply passage 315 of the cuvette 305 is placed in contact with thefluid that flows from the wound. In another embodiment, the sample isobtained without creating a wound, e.g. as is done with a saliva sample.In that case, the opening 317 of the sample supply passage 315 of thecuvette 305 is placed in contact with the fluid obtained withoutcreating a wound. The fluid is then transported through the samplesupply passage 315 and into the sample cell 310 via capillary action.The air vent passage 320 improves the capillary action by preventing thebuildup of air pressure within the cuvette and allowing the blood todisplace the air as the blood flows therein.

Other mechanisms may be employed to transport the sample to the samplecell 310. For example, wicking could be used by providing a wickingmaterial in at least a portion of the sample supply passage 315. Inanother variation, wicking and capillary action could be used togetherto transport the sample to the sample cell 310. Membranes could also bepositioned within the sample supply passage 315 to move the blood whileat the same time filtering out components that might complicate theoptical measurement performed by the whole-blood system 100.

FIGS. 16 and 16A depict one approach to constructing the cuvette 305. Inthis approach, the cuvette 305 comprises a first layer 350, a secondlayer 355, and a third layer 360. The second layer 355 is positionedbetween the first layer 350 and the third layer 360. The first layer 350forms the first sample cell window 330 and the vent 325. As mentionedabove, the vent 325 provides an escape for the air that is in the samplecell 310. While the vent 325 is shown on the first layer 350, it couldalso be positioned on the third layer 360, or could be a cutout in thesecond layer, and would then be located between the first layer 360 andthe third layer 360. The third layer 360 forms the second sample cellwindow 335.

The second layer 355 may be formed entirely of an adhesive that joinsthe first and third layers 350, 360. In other embodiments, the secondlayer may be formed from similar materials as the first and thirdlayers, or any other suitable material. The second layer 355 may also beformed as a carrier with an adhesive deposited on both sides thereof.The second layer 355 forms the sample supply passage 315, the air ventpassage 320, and the sample cell 310. The thickness of the second layer355 can be between about 1 μm and about 1.22 mm. This thickness canalternatively be between about 1 μm and about 100 μm. This thicknesscould alternatively be about 80 μm, but is preferably between about 10μm and about 50 μm. In another embodiment, the second layer thickness isabout 25 μm.

In other embodiments, the second layer 355 can be constructed as anadhesive film having a cutout portion to define the passages 315, 320,or as a cutout surrounded by adhesive.

Further information can be found in U.S. patent application Ser. No.10/055,875, filed Jan. 22, 2002, titled REAGENT-LESS WHOLE-BLOOD GLUCOSEMETER, the entirety of which is hereby incorporated by reference hereinand made a part of this specification.

II. Reagentless Whole-Blood Analyte Detection System

A. Detection Systems

FIG. 18 shows a schematic view of a reagentless whole-blood analytedetection system 400 that is similar to the whole-blood system 200discussed above, except as detailed below. The whole-blood system 400can be configured to be used near a patient. One embodiment that isconfigured to be used near a patient is a near-patient, or point-of-caretest system. Such systems provide several advantages over more complexlaboratory systems, including convenience to the patient or doctor, easeof use, and the relatively low cost of the analysis performed.

The whole-blood system 400 comprises a housing 402, a communication port405, and a communication line 410 for connecting the whole-blood system400 to an external device 420. One such external device 420 is anotheranalyte detection system, e.g., the noninvasive system 10. Thecommunication port 405 and line 410 connect the whole-blood system 400to transmit data to the external device 420 in a manner that preferablyis seamless, secure, and organized. For example, the data may becommunicated via the communications port 405 and line 410 in anorganized fashion so that data corresponding to a first user of thewhole-blood system 400 is segregated from data corresponding to otherusers. This is preferably done without intervention by the users. Inthis way, the first user's data will not be misapplied to other users ofthe whole-blood system 400. Other external devices 420 may be used, forexample, to further process the data produced by the monitor, or to makethe data available to a network, such as the Internet. This enables theoutput of the whole-blood system 400 to be made available to remotelylocated health-care professionals, as is known. Although the device 420is labeled an “external” device, the device 420 and the whole-bloodsystem 400 may be permanently connected in some embodiments.

The whole-blood system 400 is configured to be operated easily by thepatient or user. As such, the whole-blood system 400 is preferably aportable device. As used herein, “portable” means that the whole-bloodsystem 400 can be easily transported by the patient and used whereconvenient. For example, the housing 402, which is configured to houseat least a portion of the source 220 and the detector 250, is small. Inone preferred embodiment, the housing 402 of the whole-blood system 400is small enough to fit into a purse or backpack. In another embodiment,the housing 402 of the whole-blood system 400 is small enough to fitinto a pants pocket. In still another embodiment, the housing 402 of thewhole-blood system 400 is small enough to be held in the palm of a handof the user. In addition to being compact in size, the whole-bloodsystem 400 has other features that make it easier for the patient or enduser to use it. Such features include the various sample elementsdiscussed herein that can easily be filled by the patient, clinician,nurse, or doctor and inserted into the whole-blood system 400 withoutintervening processing of the sample. FIG. 18 shows that once a sampleelement, e.g., the cuvette shown, is filled by the patient or user, itcan be inserted into the housing 402 of the whole-blood system 400 foranalyte detection. Also, the whole-blood systems described herein,including the whole-blood system 400, are configured for patient use inthat they are durably designed, e.g., having very few moving parts.

In one embodiment of the whole-blood system 400, the radiation source220 emits electromagnetic radiation of wavelengths between about 3.5 μmand about 14 μm. The spectral band comprises many of the wavelengthcorresponding to the primary vibrations of molecules of interest. Inanother embodiment, the radiation source 220 emits electromagneticradiation of wavelengths between about 0.8 μm and about 2.5 μm. Inanother embodiment, the radiation source 220 emits electromagneticradiation of wavelengths between about 2.5 μm and about 20 μm. Inanother embodiment, the radiation source 220 emits electromagneticradiation of wavelengths between about 20 μm and about 100 μm. Inanother embodiment, the radiation source 220 emits radiation betweenabout 5.25 μm and about 12.0 μm. In still another embodiment theradiation source 220 emits infrared radiation between about 6.85 μm andabout 10.10 μm.

As discussed above, the radiation source 220 is modulated between aboutone-half hertz and about ten hertz in one embodiment. In anotherembodiment, the source 220 is modulated between about 2.5 hertz andabout 7.5 hertz. In another embodiment, the source 220 is modulated atabout 5 hertz. In another variation, the radiation source 220 could emitradiation at a constant intensity, i.e., as a D.C. source.

The transport of a sample to the sample cell 242 is achieved preferablythrough capillary action, but may also be achieved through wicking, or acombination of wicking and capillary action. As discussed below, one ormore flow enhancers may be incorporated into a sample element, such asthe cuvette 240 to improve the flow of blood into the sample cell 242. Aflow enhancer is any of a number of physical treatments, chemicaltreatments, or any topological features on one or more surface of thesample supply passage that helps the sample flow into the sample cell242. In one embodiment of a flow enhancer, the sample supply passage 248is made to have one very smooth surface and an opposing surface that hassmall pores or dimples. These features can be formed by a process wheregranulated detergent is spread on one surface. The detergent is thenwashed away to create the pores or dimples. Flow enhancers are discussedin more detail below. By incorporating one or more flow enhancers intothe cuvette 240, the volume of the sample supply passage 248 can bereduced, the filling time of the cuvette 240 can be reduced, or both thevolume and the filling time of the cuvette 240 can be reduced.

Where the filter 230 comprises an electronically tunable filter, a solidstate tunable infrared filter such as the one produced by ION OPTICSINC., may be used. The ION OPTICS, INC. device is a commercialadaptation of a device described in an article by James T. Daly et al.titled Tunable Narrow-Band Filter for LWIR Hyperspectral Imaging. Theentire contents of this article are hereby incorporated by referenceherein and made a part of this specification. The use of anelectronically tunable filter advantageously allows monitoring of alarge number of wavelengths in a relatively small spatial volume.

As discussed above, the filter 230 could also be implemented as a filterwheel 530, shown in FIG. 19. As with the filter 230, the filter wheel530 is positioned between the source 220 and the cuvette 240. It shouldbe understood that the filter wheel 530 can be used in connection withany other sample element as well. The filter wheel 530 comprises agenerally planar structure 540 that is rotatable about an axis A. Atleast a first filter 550A is mounted on the planar structure 540, and isalso therefore rotatable. The filter wheel 530 and the filter 550A arepositioned with respect to the source 220 and the cuvette 240 such thatwhen the filter wheel 530 rotates, the filter 550A is cyclically rotatedinto the optical path of the radiation emitted by the source 220. Thusthe filter 550A cyclically permits radiation of specified wavelengths toimpinge upon the cuvette 240. In one embodiment illustrated in FIG. 19,the filter wheel 530 also comprises a second filter 550B that issimilarly cyclically rotated into the optical path of the radiationemitted by the source 220. FIG. 19 further shows that the filter wheel530 could be constructed with as many filters as needed (i.e., up to ann.sup.th filter, 550N).

As discussed above, the filters 230, 530 permit electromagneticradiation of selected wavelengths to pass through and impinge upon thecuvette 240. Preferably, the filters 230, 530 permit radiation at leastat about the following wavelengths to pass through to the cuvette: 4.2μm, 5.25 μm, 6.12 μm, 7.4 μm, 8.0 μm, 8.45 μm, 9.25 μm, 9.65 μm, 10.4μm, 12.2 μm. In another embodiment, the filters 230, 530 permitradiation at least at about the following wavelengths to pass through tothe cuvette: 5.25 μm, 6.12 μm, 6.8 μm, 8.03 μm, 8.45 μm, 9.25 μm, 9.65μm, 10.4 μm, 12 μm. In still another embodiment, the filters 230, 530permit radiation at least at about the following wavelengths to passthrough to the cuvette: 6.85 μm, 6.97 μm, 7.39 μm, 8.23 μm, 8.62 μm,9.02 μm, 9.22 μm, 9.43 μm, and 10.10 μm. The sets of wavelengths recitedabove correspond to specific embodiments within the scope of thisdisclosure. Other sets of wavelengths can be selected within the scopeof this disclosure based on cost of production, development time,availability, and other factors relating to cost, manufacturability, andtime to market of the filters used to generate the selected wavelengths.

The whole-blood system 400 also comprises a signal processor 260 that iselectrically connected to the detector 250. As discussed above, thedetector 250 responds to radiation incident upon the active surface 254by generating an electrical signal that can be manipulated in order toanalyze the radiation spectrum. In one embodiment, as described above,the whole-blood system 400 comprises a modulated source 220 and a filterwheel 530. It that embodiment, the signal processor 260 includes asynchronous demodulation circuit to process the electrical signalsgenerated by the detector 250. After processing the signals of thedetector 250, the signal processor 260 provides an output signal to adisplay 448.

In one embodiment of the whole-blood system 400, the display 448 is adigital display, as is illustrated in FIG. 13. In another embodiment,the display 448 is an audible display. This type of display could beespecially advantages for users with limited vision, mobility, orblindness. In another embodiment, the display 448 is not part of thewhole-blood system 400, but rather is a separate device. As a separatedevice, the display may be permanently connected to or temporarilyconnectable to the whole-blood system 448. In one embodiment, thedisplay is a portable computing device, commonly known as a personaldata assistant (“PDA”), such as the one produced by PALM, INC. under thenames PalmPilot, PalmIII, PalmV, and PalmVII.

FIG. 18A is a schematic view of a reagentless detection system 450(“reagentless system”) that has a housing 452 enclosing, at leastpartially, a reagentless whole-blood analyte detection subsystem 456(“whole-blood subsystem”) and a noninvasive subsystem 460. As discussedabove, the whole-blood subsystem 456 is configured to obtain a sample ofwhole-blood. This can be done using the sample extractor 280 discussedabove in connection with FIG. 13. As discussed above, samples of otherbiological fluids can also be used in connection with the whole-bloodsystem 450. Once extracted, the sample is positioned in the sample cell242, as discussed above. Then, optical analysis of the sample can beperformed. The noninvasive subsystem 460 is configured to function asdescribed above in connection with FIGS. 1-12. In one mode of operation,the reagentless system 450 can be operated to employ either thewhole-blood subsystem 456 or the noninvasive subsystem 460 separately.The reagentless system 450 can be configured to select one subsystem orthe other depending upon the circumstances, e.g., whether the user hasrecently eaten, whether an extremely accurate test is desired, etc. Inanother mode of operation, the reagentless system 450 can operate thewhole-blood subsystem 456 and the noninvasive subsystem 460 in acoordinated fashion. For example, in one embodiment, the reagentlesssystem 450 coordinates the use of the subsystems 456, 460 whencalibration is required. In another embodiment, the reagentless system450 is configured to route a sample either to the whole-blood subsystem456 through a first selectable sample supply passage or to thenoninvasive subsystem 460 through a second selectable sample supplypassage after the sample has been obtained. The subsystem 460 may beconfigured with an adapter to position the whole-blood sample on thewindow for a measurement.

FIG. 20A-20C illustrate another approach to constructing a cuvette 605for use with the whole-blood system 200. In this embodiment, a firstportion 655 is formed using an injection molding process. The firstportion 655 comprises a sample cell 610, a sample supply passage 615, anair vent passage 620, and the second sample cell window 335. The cuvette605 also comprises a second portion 660 that is configured to beattached to the first portion 655 to enclose at least the sample cell610 and the sample supply passage 615. The second portion 660 comprisesthe first sample cell window 330 and preferably also encloses at least aportion of the air vent passage 620. The first portion 655 and thesecond portion 660 are preferably joined together by a welding processat welding joints 665. Although four welding joints 665 are shown, itshould be understood that fewer or more than four welding joints couldbe used. As will be understood, other techniques also could be used tosecure the portions 655, 660.

Yet another approach to the construction of the cuvette 240 is toproduce it using a wafer fabrication process. FIG. 21 illustrates oneembodiment of a process to produce a cuvette 755 usingmicro-electromechanical system machining techniques, such as waferfabrication techniques. In a step 710, a wafer is provided that is madeof a material having acceptable electromagnetic radiation transmissionproperties, as discussed above. The wafer preferably is made of siliconor germanium. Preferably in a next step 720, a second wafer is providedthat is made of a material having acceptable electromagnetic radiationtransmission properties. The second wafer may be a simple planar portionof the selected material. Preferably, in a next step 730, an etchingprocess is used to create a multiplicity of cuvette subassemblies, eachsubassembly having a sample supply passage, an air vent passage, and asample cell. Conventional etching processes may be employed to etchthese structures in the wafer, with an individual etching subassemblyhaving an appearance similar to the first portion 655 shown in FIG. 20C.Preferably, in a next step 740, the second wafer is attached, bonded,and sealed to the first wafer to create a wafer assembly that encloseseach of the sample supply passages, sample cells, and the air ventpassages. This process creates a multiplicity of cuvettes connected toeach other. Preferably in a next step 750, the wafer assembly isprocessed, e.g., machined, diced, sliced, or sawed, to separate themultiplicity of cuvettes into individual cuvettes 755. Although thesteps 710-750 have been set forth in a specific order, it should beunderstood that the steps may be performed in other orders within thescope of the method.

In one embodiment, the cuvettes 755 made according to the process ofFIG. 21 are relatively small. In another embodiment, the cuvettes 755are about the size of the cuvettes 305. If the cuvettes 755 are small,they could be made easier to use by incorporating them into a disposablesample element handler 780, shown in FIG. 22. The disposable sampleelement handler 780 has an unused sample element portion 785 and a usedsample element portion 790. When new, the unused cuvette portion 785 maycontain any number of sample elements 757. For the first use of thesample element handler 780 by a user, a first sample element 757A isadvanced to a sample taking location 795. Then a user takes a sample inthe manner described above. An optical measurement is performed using awhole-blood system, such as the system 200. Once the measurement iscomplete, the used sample element 757A can be advanced toward the usedsample element portion 790 of the disposable sample element handler 780,as the next sample element 757B is advanced to the sample takinglocation 795. Once the last sample element 757N is used, the disposablesample element handler 780 can be discarded, with the biohazardousmaterial contained in the used sample element portion 790. In anotherembodiment, once the sample is taken, the sample element 757A isadvanced into the housing 402 of the test system 400. In someembodiments, the sample element handler 780 can be automaticallyadvanced to the sample taking location 795, and then automaticallyadvanced to into the housing 402.

As discussed above in connection with FIGS. 15-17, the air vent 325allows air in the cuvette 305 to escape, thereby enhancing the flow ofthe sample from the appendage 290 into the sample cell 310. Otherstructures, referred to herein as “flow enhancers,” could also be usedto enhance the flow of a sample into a sample cell 310. FIG. 23Aillustrates one embodiment of a cuvette 805 with a flow enhancer. Thecuvette 805 comprises a sample cell 810, a sample supply passage 815,and a seal 820. A sample extractor 880 can be incorporated into orseparate from the cuvette 805.

The seal 820 of the cuvette 805 maintains a vacuum within the samplecell 810 and the sample supply passage 815. The seal 820 also provides abarrier that prevents contaminants from entering the cuvette 805, butcan be penetrated by the sample extractor 880. The seal 820 mayadvantageously create a bond between the tissue and the cuvette 805 toeliminate extraneous sample loss and other biological contamination.Although many different materials could be used to prepare the seal 820,one particular material that could be used is DuPont's TYVEK material.The cuvette 805 not only enhances sample flow, but also eliminates theproblem of sample spillage that may be found with capillary collectionsystems relying upon a vent to induce the collection flow. The flowenhancement approach applied to the cuvette 805 could also be applied toother sample elements.

FIG. 23B is a schematic illustration of a cuvette 885 that is similar tothat shown in FIG. 23A, except as described below. The cuvette 885comprises one or a plurality of small pores that allow air to pass fromthe inside of the cuvette 885 to the ambient atmosphere. These smallpores function similar to the vent 325, but are small enough to preventthe sample (e.g., whole-blood) from spilling out of the cuvette 885. Thecuvette 885 could further comprise a mechanical intervention bloodacquisition system 890 that comprises an external vacuum source (i.e., apump), a diaphragm, a plunger, or other mechanical means to improvesample flow in the cuvette 885. The system 890 is placed in contact withthe small pores and draws the air inside the cuvette 885 out of thecuvette 885. The system 890 also tends to draw the blood into thecuvette 885. The flow enhancement technique applied to the cuvette 885could be applied to other sample elements as well.

Another embodiment of a flow enhancer is shown in FIGS. 24A and 23B. Acuvette 905 is similar to the cuvette 305, comprising the sample cell310 and the windows 330, 335. As discussed above, the windows couldcomprise sample cell walls. The cuvette also comprises a sample supplypassage 915 that extends between a first opening 917 at an outer edge ofthe cuvette 905 and a second opening 919 at the sample cell 310 of thecuvette 905. As shown in FIG. 24B, the sample supply passage 915comprises one or more ridges 940 that are formed on the top and thebottom of the sample supply passage 915. In one variation, the ridges940 are formed only on the top, or only on the bottom of the samplesupply passage 915. The undulating shape of the ridges 940advantageously enhances flow of the sample into the sample supplypassage 915 of the cuvette 905 and may also advantageously urge thesample to flow into the sample cell 310.

Other variations of the flow enhancer are also contemplated. Forexample, various embodiments of flow enhancers may include physicalalteration, such as scoring passage surfaces. In another variation, achemical treatment, e.g., a surface-active chemical treatment, may beapplied to one or more surfaces of the sample supply passage to reducethe surface tension of the sample drawn into the passage. As discussedabove, the flow enhancers disclosed herein could be applied to othersample elements besides the various cuvettes described herein.

As discussed above, materials having some electromagnetic radiationabsorption in the spectral range employed by the whole-blood system 200can be used to construct portions of the cuvette 240. FIG. 25 shows awhole-blood analyte detection system 1000 that, except as detailedbelow, may be similar to the whole-blood system 200 discussed above. Thewhole-blood system 1000 is configured to determine the amount ofabsorption by the material used to construct a sample element, such as acuvette 1040. To achieve this, the whole-blood system 1000 comprises anoptical calibration system 1002 and an optical analysis system 1004. Asshown, the whole-blood system 1000 comprises the source 220, which issimilar to that of the whole-blood system 200. The whole-blood system1000 also comprises a filter 1030 that is similar to the filter 230. Thefilter 1030 also splits the radiation into two parallel beams, i.e.,creates a split beam 1025. The split beam 1025 comprises a calibrationbeam 1027 and an analyte transmission beam 1029. In another variation,two sources 220 may be used to create two parallel beams, or a separatebeam splitter may be positioned between the source 220 and the filter1030. A beam splitter could also be positioned downstream of the filter1030, but before the cuvette 1040. In any of the above variations, thecalibration beam 1027 is directed through a calibration portion 1042 ofthe cuvette 1040 and the analyte transmission beam 1029 is directedthrough the sample cell 1044 of the cuvette 1040.

In the embodiment of FIG. 25, the calibration beam 1027 passes throughthe calibration portion 1042 of the cuvette 1040 and is incident upon anactive surface 1053 of a detector 1052. The analyte transmission beam1029 passes through the sample cell 1044 of the cuvette 1040 and isincident upon an active surface 1055 of a detector 1054. The detectors1052, 1054 may be of the same type, and may use any of the detectiontechniques discussed above. As described above, the detectors 1052, 1054generate electrical signals in response to the radiation incident upontheir active surfaces 1053, 1055. The signals generated are passed tothe digital signal processor 1060, which processes both signals toascertain the radiation absorption of the cuvette 1040, corrects theelectrical signal from the detector 1054 to eliminate the absorption ofthe cuvette 1040, and provides a result to the display 484. In oneembodiment, the optical calibration system 1002 comprises thecalibration beam 1027 and the detector 1052 and the optical analysissystem 1004 comprises the analyte transmission beam 1029 and thedetector 1054. In another embodiment, the optical calibration system1002 also comprises the calibration portion 1042 of the cuvette 1040 andthe optical analysis system 1004 also comprises the analysis portion1044 of the cuvette 1040.

FIG. 26 is a schematic illustration of another embodiment of areagentless whole-blood analyte detection system 1100 (“whole-bloodsystem”). FIG. 26 shows that a similar calibration procedure can becarried out with a single detector 250. In this embodiment, the source220 and filter 230 together generate a beam 1125, as described above inconnection with FIG. 13. An optical router 1170 is provided in theoptical path of the beam 1125. The router 1170 alternately directs thebeam 1125 as a calibration beam 1127 and as an analyte transmission beam1129. The calibration beam 1127 is directed through the calibrationportion 1042 of the cuvette 1040 by the router 1170. In the embodimentof FIG. 26, the calibration beam 1127 is thereafter directed to theactive surface 254 of the detector 250 by a first calibration beamoptical director 1180 and a second calibration beam optical director1190. In one embodiment, the optical directors 1180, 1190 are reflectivesurfaces. In another variation, the optical directors 1180, 1190 arecollection lenses. Of course, other numbers of optical directors couldbe used to direct the beam onto the active surface 254.

As discussed above, the analyte transmission beam 1129 is directed intothe sample cell 1044 of the cuvette 1040, transmitted through thesample, and is incident upon the active surface 254 of the detector 250.A signal processor 1160 compares the signal generated by the detector250 when the calibration beam 1127 is incident upon the active surface254 and when the analyte transmission beam 1129 is incident upon theactive surface. This comparison enables the signal processor 1160 togenerate a signal that represents the absorption of the sample in thesample cell 1044 only, i.e., with the absorption contribution of thecuvette 1040 eliminated. This signal is provided to a display 484 in themanner described above. Thus, the absorbance of the cuvette 1040 itselfcan be removed from the absorbance of the cuvette-plus-sample observedwhen the beam 1029 is passed through the sample cell and detected at thedetector 250. As discussed above in connection with FIG. 25, thewhole-blood system 1100 comprises an optical calibration system 1196 andan optical analysis system 1198. The optical calibration system 1196could comprise the router 1170, the optical directors 1180, 1190, andthe detector 250. The optical analysis system 1198 could comprise therouter 1170 and the detector 250. In another embodiment, the opticalanalysis system 1198 also comprises the analysis portion 1044 of thecuvette 1040 and the optical calibration system 1196 also comprises thecalibration portion 1042 of the cuvette 1040. The cuvette 1040 is butone form of a sample element that could be used in connection with thesystems of FIGS. 25 and 26.

FIG. 27 is a schematic illustration of a cuvette 1205 configured to beused in the whole-blood systems 1000, 1100. The calibration portion 1242is configured to permit the whole-blood systems 1000, 1100 to estimatethe absorption of only the windows 330, 335 without reflection orrefraction. The cuvette 1205 comprises a calibration portion 1242 and asample cell 1244 having a first sample cell window 330 and a secondsample cell window 335. The calibration portion 1242 comprises a window1250 having the same electromagnetic transmission properties as thewindow 330 and a window 1255 having the same electromagnetictransmission properties as the window 335. As discussed above, thewindows 1250, 1255 is a form of a sample cell wall and there need not betwo windows in some embodiments. In one embodiment, the calibrationportion 1242 is necked-down from the sample cell 1244 so that theseparation of the inner surfaces of the windows 1250, 1255 issignificantly less than the separation of the inner surface 332 of thewindow 330 and the surface 337 of the window 335 (i.e., the dimension Tshown in FIG. 17). Although the calibration portion 1242 is necked-down,the thickness of the windows 1250, 1255 preferably is the same as thewindows 330, 335.

By reducing the separation of the windows 1250, 1255 in the calibrationportion 1242, error in the estimate of the absorption contribution bythe windows 330, 335 of the sample cell 1240 can be reduced. Such errorcan be caused, for example, by scattering of the electromagneticradiation of the beam 1027 or the beam 1127 by molecules located betweenthe windows 1250, 1255 as the radiation passes through the calibrationportion 1242. Such scattering could be interpreted by the signalprocessors 1060, 1160 as absorption by the windows 1250, 1255.

In another variation, the space between the windows 1250, 1255 can becompletely eliminated. In yet another variation, the signal processor1060, 1160 can include a module configured to estimate any error inducedby having a space between the windows 1250, 1255. In that case, thecalibration portion 1242 need not be necked down at all and the cuvette1240, as well as the windows 1250, 1255 can have generally constantthickness along their lengths.

FIG. 28 is a plan view of one embodiment of a cuvette 1305 having asingle motion lance 1310 and a sample supply passage 1315. The lance1310 can be a metal lance, a lance made of sharpened plastic, or anyother suitable rigid material. The lance 1310 works like a miniaturerazor-blade to create a slice, which can be very small or amicrolaceration, into an appendage, such as a finger, forearm, or anyother appendage as discussed above. The lance 1310 is positioned in thecuvette 1305 such that a single motion used to create the slice in theappendage also places an opening 1317 of the sample supply passage 1315at the wound. This eliminates the step of aligning the opening 1317 ofthe sample supply passage 1315 with the wound. This is advantageous forall users because the cuvette 1305 is configured to receive a very smallvolume of the sample and the lance 1310 is configured to create a verysmall slice. As a result, separately aligning the opening 1317 and thesample of whole-blood that emerges from the slice can be difficult. Thisis especially true for users with limited fine motor control, such aselderly users or those suffering from muscular diseases.

FIG. 28A is a plan view of another embodiment of a cuvette 1355 having asingle motion lance 1360, a sample supply passage 1315, and an opening1317. As discussed above, the single motion lance 1360 can be a metallance, a lance made of sharpened plastic, or any other suitable rigidmaterial. As with the lance 1310, the lance 1360 works like a miniaturerazor-blade to create a tiny slice, or a microlaceration into anappendage. The single motion lance 1360 also has an appendage piercingend that has a first cutting implement 1365 and a second cuttingimplement 1370 that converge at a distal end 1375. Between the distalend 1375 and the inlet 1317, an divergence 1380 is formed. The singlemotion lance 1360 is positioned in the cuvette 1305 such that a singlemotion creates the slice in the appendage and places the opening 1317 ofthe sample supply passage 1315 at the wound. The divergence 1380 isconfigured to create a wound that is small enough to minimize the painexperienced by the user but large enough to yield enough whole-blood tosufficiently fill the cuvette 1355. As discussed above in connectionwith the cuvette 1305, the cuvette 1355 eliminates the need toseparately create a slice and to align the opening 1317 of the cuvette1355.

FIG. 29 is a plan view of another embodiment of a cuvette 1405 having asingle motion lance 1410 that is constructed in any suitable manner, asdiscussed above. In this embodiment, the single motion lance 1410 ispositioned adjacent the sample supply passage 1415. The opening 1417 ofthe sample supply passage 1415 is located such that the cuvette 1405 canbe placed adjacent an appendage, moved laterally to create a slice inthe appendage, and aligned. As may be seen, the width of the lance 1410is small compared to the width of the sample supply passage 1415. Thisassures that the movement of the cuvette 1405 that creates the slice inthe appendage also positions the opening 1417 of the sample supplypassage 1415 at the wound. As discussed above in connection with thecuvette 1305, the cuvette 1405 eliminates the need to separately createa slice and to align the opening 1417 of the cuvette 1405.

FIGS. 31-32A illustrate another embodiment of a reagentless sampleelement 1502 which can be used in connection with the whole-bloodsystems 200, 400, 450, 1000 and 1100, or separately therefrom. Thereagentless sample element 1502 is configured for reagentlessmeasurements of analyte concentrations performed near a patient. Thisprovides several advantages over more complex laboratory systems,including convenience to the patient or physician, ease of use, and arelatively low cost of the analysis performed. Additional information onreagent-based sample elements can be found in U.S. Pat. No. 6,143,164,issued Nov. 7, 2000, titled SMALL VOLUME IN VITRO ANALYTE SENSOR, theentirety of which is hereby incorporated by reference herein and made apart of this specification.

The sample element 1502 comprises a cuvette 1504 retained within a pairof channels 1520, 1522 of a housing 1506. As shown in FIG. 31, thehousing 1506 further includes an integrated lance 1507 comprising aresilient deflectable strip 1508 and a distal lancing member 1524. Thedistal lancing member 1524 comprises a sharp cutting implement made ofmetal or other rigid material, which can form an opening in anappendage, such as the finger 290, to make whole-blood available to thecuvette 1504. It should be understood that other appendages could beused to draw the sample, including but not limited to the forearm,abdomen, or anywhere on the hands other than the fingertips. It will beappreciated that the integrated lance 1507 facilitates single-handedoperation of the sample element 1502 while at the same time requiringfewer motions of the sample element 1502 during sample extractionprocedures.

It is contemplated that in various other embodiments, the integratedlance 1507 may comprise a laser lance, iontophoretic sampler, gas-jet,fluid-jet or particle-jet perforator, or any other suitable device. Onesuitable laser lance is the Lasette Plus® produced by Cell RoboticsInternational, Inc. of Albuquerque, N. Mex. It is further contemplatedthat when a laser lance, iontophoretic sampler, gas-jet or fluid-jetperforator is used, the integrated lance 1507 can be incorporated intothe whole-blood system 200, incorporated into the housing 1506 orutilized as a separate device. Additional information on laser lancescan be found in above-mentioned U.S. Pat. No. 5,908,416. One suitablegas-jet, fluid-jet or particle-jet perforator is disclosed in theabove-mentioned U.S. Pat. No. 6,207,400, and one suitable iontophoreticsampler is disclosed in the above-mentioned U.S. Pat. No. 6,298,254.

The cuvette 1504 comprises a first plate 1510, a second plate 1512 and apair of spacers 1514, 1514′. As shown most clearly in FIGS. 32A and 33,the spacers 1514, 1514′ are disposed between the first and second plates1510, 1512 such that a sample supply passage 1518 is definedtherebetween and has an opening 1519 (see FIG. 32) at a distal end 1503of the cuvette 1504. The plates 1510, 1512 and the spacers 1514, 1514′are glued, welded or otherwise fastened together by use of any suitabletechnique. The housing provides mechanical support to the plates 1510,1512 and the spacers 1514, 1514′, and facilitates holding the cuvette1504 when used separately from the whole-blood system200/400/450/1000/1100.

The spacers 1514, 1514′ may be formed entirely of an adhesive that joinsthe first and second plates 1510, 1512. In other embodiments, thespacers 1514, 1514′ may be formed from similar materials as the plates1510, 1512, or any other suitable material. The spacers 1514, 1514′ mayalso be formed as carriers with an adhesive deposited on both sidesthereof.

As shown in FIG. 33, the first plate 1510 comprises a first window 1516and the second plate 1512 comprises a second window 1516′. The first andsecond windows 1516, 1516′ are preferably optically transmissive in therange of electromagnetic radiation that is emitted by the source 220, orthat is permitted to pass through the filter 230. In one embodiment, thematerial comprising the windows 1516, 1516′ is completely transmissive,i.e.; the material does not absorb any of the incident electromagneticradiation from the source 220 and filter 230. In another embodiment, thematerial comprising the windows 1516, 1516′ exhibits negligibleabsorption in the electromagnetic range of interest. In yet anotherembodiment, the absorption of the material comprising the windows 1516,1516′ is not negligible, rather the absorption is known and stable for arelatively long period of time. In another embodiment, the absorption ofthe windows 1516, 1516′ is stable for only a relatively short period oftime, but the whole-blood system 200 may be configured to detect theabsorption of the material and eliminate it from the analyte measurementbefore the material properties undergo any measurable changes.

In one embodiment, the first and second windows 1516, 1516′ are made ofpolypropylene. In another embodiment, the windows 1516, 1516′ are madeof polyethylene. As mentioned above, polyethylene and polypropylene arematerials having particularly advantageous properties for handling andmanufacturing, as is known in the art. Additionally, these plastics canbe arranged in a number of structures, e.g., isotactic, atactic andsyndiotactic, which may enhance the flow characteristics of the samplein the sample element 1502. Preferably, the windows 1516, 1516′ are madeof a durable and easily manufacturable material, such as theabove-mentioned polypropylene or polyethylene, silicon, or any othersuitable material. Furthermore, the windows 1516, 1516′ can be made ofany suitable polymer which can be isotactic, atactic or syndiotactic instructure.

Alternatively, the entirety of the first and second plates 1510, 1512may be made of a transparent material, such as polypropylene orpolyethylene, as discussed above. In this embodiment, each of the plates1510, 1512 is formed from a single piece of transparent material, andthe windows 1516, 1516′ are defined by the positions of the spacers1514, 1514′ between the plates 1510, 1512 and the longitudinal distancealong the sample supply passage 1518 which is analyzed. It will beappreciated that forming the entirety of the plates 1510, 1512 oftransparent material advantageously simplifies manufacturing of thecuvette 1504.

As illustrated in FIGS. 32A and 32B, the first and second windows 1516,1516′ are positioned on the plates 1510, 1512 such that the windows1516, 1516′ and the spacers 1514, 1514′ define a chamber 1534. Thechamber 1534 is defined between an inner surface 1517 of the firstwindow 1516 and an inner surface 1517′ of the second window 1516′ aswell as, where spacers are employed, an inner surface 1515 of the spacer1514, and an inner surface 1515′ of the spacer 1514′. Distal of thechamber 1534 is the sample supply passage 1518 and proximal of thechamber 1534 is a vent 1536. It will be appreciated that the chamber1534 and the vent 1536 are formed by the distal extension of the samplesupply passage 1518 along the length of the spacers 1514, 1514′. Asillustrated in FIG. 32B, dashed lines indicate the boundaries betweenthe chamber 1534, the sample supply passage 1518, and the vent 1536. Theperpendicular distance T between the inner surfaces 1517, 1517′comprises an optical pathlength which, in one embodiment, can be betweenabout 1 μm and less than about 1.22 mm. Alternatively, the opticalpathlength can be between about 1 μm and about 100 μm. The opticalpathlength could still alternatively be about 80 μm, or between about 10μm and about 50 μm. In another embodiment, the optical pathlength isabout 25 μm. The thickness of each window is preferably as small aspossible without overly weakening the chamber 1534 or the cuvette 1504.

Because the sample elements depicted in FIGS. 31-35 are reagentless, andare intended for use in reagentless measurement of analyteconcentration, the inner surfaces 1515, 1515′, 1517, 1517′ which definethe chamber 1534, and/or the volume of the chamber 1534 itself, areinert with respect to any of the body fluids which may be drawn thereinfor analyte concentration measurements. In other words, the materialforming the inner surfaces 1515, 1515′, 1517, 1517′, and/or any materialcontained in the chamber 1534, will not react with the body fluid in amanner which will significantly affect any measurement made of theconcentration of analyte(s) in the sample of body fluid with thewhole-blood system 200/400/450/1000/1100 or any other suitable system,for about 15-30 minutes following entry of the sample into the chamber1534. Accordingly, the chamber 1534 comprises a reagentless chamber.

In one embodiment, the plates 1510, 1512 and the spacers 1514, 1514′ aresized so that the chamber 1534 has a volume of about 0.5 μL. In anotherembodiment, the plates 1510, 1512 and the spacers 1514, 1514′ are sizedso that the total volume of body fluid drawn into the cuvette 1504 is atmost about 1 μL. In still another embodiment, the chamber 1534 may beconfigured to hold no more than about 1 μL of body fluid. As will beappreciated by one of ordinary skill in the art, the volume of thecuvette 1504/chamber 1534/etc. may vary, depending on several variables,such as, by way of example, the size and sensitivity of the detectorsused in conjunction with the cuvette 1504, the intensity of theradiation passed through the windows 1516, 1516′, the expected flowproperties of the sample and whether or not flow enhancers (discussedabove) are incorporated into the cuvette 1504. The transport of bodyfluid into the chamber 1534 may be achieved through capillary action,but also may be achieved through wicking, or a combination of wickingand capillary action.

In operation, the distal end 1503 of the cuvette 1504 is placed incontact with the appendage 290 or other site on the patient's bodysuitable for acquiring a body fluid 1560 (FIG. 32C). The body fluid 1560may comprise whole-blood, blood components, interstitial fluid,intercellular fluid, saliva, urine, sweat and/or other organic orinorganic materials from a patient. The resilient deflectable strip 1508is then pressed and released, so as to momentarily push the lancingmember distally into the appendage 290, thereby creating a small wound.Once the wound is made, contact between the cuvette 1504 and the woundis maintained such that fluid flowing from the wound enters the samplesupply passage 1518. In another embodiment, the body fluid 1560 may beobtained without creating a wound, e.g. as is done with a saliva sample.In that case, the distal end of the sample supply passage 1518 is placedin contact with the body fluid 1560 without creating a wound. Asillustrated in FIG. 32C, the body fluid 1560 is then transported throughthe sample supply passage 1518 and into the chamber 1534. It will beappreciated that the body fluid 1560 may be transported through thesample supply passage 1518 and into the chamber 1534 via capillaryaction and/or wicking, depending on the precise structure(s) employed.The vent 1536 allows air to exit proximally from the cuvette 1504 as thebody fluid 1560 displaces air within the sample supply passage 1518 andthe chamber 1534. This prevents a buildup of air pressure within thecuvette 1504 as the body fluid 1560 flows into the chamber 1534.

Other mechanisms may be employed to transport the body fluid 1560 to thechamber 1534. For example, wicking may be used by providing a wickingmaterial in at least a portion of the sample supply passage 1518. Inanother embodiment, wicking and capillary action may be used inconjunction to transport the body fluid 1560 to the chamber 1534.Membranes also may be positioned within the sample supply passage 1518to move the body fluid 1560 while at the same time filtering outcomponents that might complicate the optical measurement performed bythe whole-blood system 200.

As shown in FIG. 32C, once the body fluid 1560 has entered the chamber1534, the cuvette 1504 is installed in any one of the whole-bloodsystems 200/400/450/1000/1100 or other similar optical measurementsystem. When the cuvette 1504 is installed in the whole-blood system200, the chamber 1534 is located at least partially within the opticalpath 243 between the radiation source 220 and the detector 250. Thus,when radiation is emitted from the source 220 through the filter 230(FIG. 13) and the chamber 1534 of the cuvette 1504, the detector 250detects the radiation signal strength at the wavelength(s) of interest.Based on this signal strength, the signal processor 260 determines thedegree to which the body fluid 1560 in the chamber 1534 absorbsradiation at the detected wavelength(s). The concentration of theanalyte of interest is then determined from the absorption data via anysuitable spectroscopic technique.

In one embodiment, a method for measuring an analyte concentrationwithin a patient's tissue comprises placing the distal end 1503 of thesample element 1502 against a withdrawal site on the patient's body. Inone embodiment, the withdrawal site is a fingertip of the appendage 290.In another embodiment, the withdrawal site may be any alternate-sitelocation on the patient's body suitable for measuring analyteconcentrations, such as, by way of example, the forearm, abdomen, oranywhere on the hand other than the fingertip.

Once the distal end 1503 is placed in contact with a suitable withdrawalsite, the integrated lance 1507 shown in FIG. 31 is used to lance thewithdrawal site, thereby creating a small wound. While the sampleelement 1502 is maintained in stationary contact with the withdrawalsite, without moving the distal end 1503 or the cuvette 1504, the bodyfluid 1560 (FIG. 32C) flows from the withdrawal site, enters the openingof the sample supply passage 1518 and is transported into the samplechamber 1534. Transport of the body fluid 1560 into the chamber 1534 isachieved through capillary action, but also may be achieved throughwicking, or a combination of wicking and capillary action, dependingupon the particular structures and/or enhancers utilized in conjunctionwith the sample element 1502. In one embodiment, the cuvette 1504 isconfigured to withdraw no more than about 1 μL of the body fluid 1560.In another embodiment, the chamber 1534 is configured to hold at mostabout 0.5 μL of the body fluid 1560. In still another embodiment, thechamber 1534 may be configured to hold no more than about 1 μL of thebody fluid 1560.

Once the body fluid 1560 is withdrawn into the chamber 1534, asdescribed above, the sample element 1502 is removed from the withdrawalsite and the cuvette 1504 is removed from the housing 1506. The cuvette1504 is then inserted into the any one of the whole-blood systems200/400/450/1000/1100, or other similar system, such that the chamber1534 is located in the optical path 243. Preferably, the chamber 1534 issituated within the optical path 243 such that the windows 1516, 1516′are oriented substantially perpendicular to the optical path 243 asshown in FIG. 32C. When the cuvette 1504 is inserted into thewhole-blood system 200, the chamber 1534 is located between theradiation source 220 and the detector 250. The analyte concentrationwithin the body fluid 1560 is then measured by using the whole-bloodsystem 200, as discussed in detail above with reference to FIG. 13.

FIGS. 34A and 34B are perspective views illustrating another embodimentof a cuvette 1530 having an integrated lancing member. The cuvette 1530is substantially similar to the cuvette 1504 of FIGS. 31-33, with theexception that the cuvette 1530 comprises a first plate 1532 having achannel 1538 which receives a lancing member 1524. The channel 1538serves as a longitudinal guide for the lancing member 1524, whichensures that the lancing member 1524 does not move transversely when itis used to create a wound, as described above. The channel 1538 alsoplaces the lancing member 1524 in closer proximity of the opening of thesample supply passage 1518. This facilitates entry of the body fluidinto the sample supply passage 1518, when the lancing member 1524 isused to create a wound, without the cuvette 1530 having to be movedaround on the wound site.

FIG. 35 illustrates another embodiment of a reagentless sample element1550 which can be used in connection with the whole-blood200/400/450/1000/1100, or separately therefrom. The sample element 1550comprises a cuvette 1504 retained within a pair of channels 1520, 1522of a housing 1556. The sample element 1550 is substantially similar tothe sample element 1502 of FIGS. 31 through 32B, with the exception thatthe housing 1556 includes a sample extractor 1552. In variousembodiments, the sample extractor 1552 may comprise a lance, laserlance, iontophoretic sampler, gas-jet, fluid-jet or particle-jetperforator, ultrasonic enhancer (used with or without a chemicalenhancer), or any other suitable device. Accordingly, the lance 1524shown in FIG. 31 is to be considered a sample extractor as well.Furthermore, it is to be understood that, as with the sample element1502 illustrated in FIG. 31, the sample element 1550 of FIG. 35 isconfigured to withdraw at most about 1 μL of the body fluid 1560.Likewise, a chamber 1534 of the sample element 1550 is configured tohold no more than about 0.5 μL of the body fluid 1560. In anotherembodiment, the chamber 1534 may be configured to hold no more thanabout 1 μL of the body fluid 1560.

As shown in FIG. 35, the sample extractor 1552 has an associatedoperating path 1554 along which acts the sample extraction mechanism(e.g., laser beam, fluid jet, particle jet, lance tip, electricalcurrent) of the sample extractor 1552 when acting on an appendage, suchas the finger 290, to make whole-blood and/or other fluid available tothe cuvette 1504. It should be understood that other appendages could beused to draw the sample, including but not limited to the forearm.

As shown in FIG. 35, the sample extractor 1552 may comprise a part ofthe housing 1556 so that the opening 1519 of the supply passage 1518,and the chamber 1534, is positioned near the operating path 1554 uponinstallation of the cuvette 1504 in the housing 1556. This arrangementensures that fluid extracted by action of the sample extractor 1552along the operating path 1554 will flow into the supply passage 1518 andthe chamber 1534 without need to move the cuvette 1504 to the withdrawalsite on the patient. If a laser lance, iontophoretic sampler, gas-jet orfluid-jet perforator is used as the sample extractor 1552, it mayalternatively be incorporated into the whole-blood system 200.

In one embodiment, a method for using the sample element 1550 to measurean analyte concentration within a patient's tissue comprises placing thedistal end 1503 of the sample element 1502 against a withdrawal site onthe patient's body. In one embodiment, the withdrawal site is afingertip of the appendage 290. In another embodiment, the withdrawalsite may be any alternate-site location on the patient's body suitablefor measuring analyte concentrations, such as, by way of example, theforearm, abdomen, or anywhere on the hand other than the fingertip.

Once the distal end 1503 is placed in contact with a suitable withdrawalsite, the sample extractor 1552 is used to cause a sample of body fluidto flow from the withdrawal site. As mentioned above, the body fluid1560 extracted by use of the sample extractor 1552 may comprisewhole-blood, blood components, interstitial fluid or intercellularfluid.

While the sample element 1550 is maintained in stationary contact withthe withdrawal site, without moving the distal end 1503 or the cuvette1504, the body fluid 1560 flows from the withdrawal site, enters theopening 1519 of the sample supply passage 1518 and transports into thesample chamber 1534. In one embodiment, transport of the body fluid 1560into the chamber 1534 is achieved through capillary action, but also maybe achieved through wicking, or a combination of wicking and capillaryaction, depending upon the particular structures and/or enhancersutilized in conjunction with the sample element 1550. As with thecuvette 1504 (FIG. 31), the cuvette 1550 is configured to withdraw nomore than about 1 μL of the body fluid 1560, and the chamber 1534 isconfigured to hold at most about 0.5 μL of the body fluid 1560. Inanother embodiment, the chamber 1534 may be configured to hold no morethan about 1 μL of the body fluid 1560.

Once the body fluid 1560 is withdrawn into the chamber 1534, the sampleelement 1550 is removed from the withdrawal site and the cuvette 1504 isremoved from the housing 1556. The cuvette 1504 is then inserted intothe any one of the whole-blood system 200/400/450/1000/1100, or othersimilar system, such that the optical path 243 passes through thechamber 1534. Preferably, the chamber 1534 is situated within theoptical path 243 such that the windows 1516, 1516′ are orientedsubstantially perpendicular to the optical path 243 as shown in FIG.32C. When the cuvette 1504 is inserted into the whole-blood system 200,the chamber 1534 is located between the radiation source 220 and thedetector 250. The analyte concentration within the body fluid 1560 isthen measured by using the whole-blood system 200, as discussed indetail above with reference to FIG. 13.

B. Advantages and Other Uses

The whole-blood systems described herein have several advantages anduses, in addition to those already discussed above. The whole-bloodsystems described herein are very accurate because they opticallymeasure an analyte of interest. Also, the accuracy of the whole-bloodsystems can be further improved without the need to draw multiple bloodsamples. In a reagent-based technique, a blood sample is brought intocontact with a reagent on a test strip, the prescribed chemical reactionoccurs, and some aspect of that reaction is observed. The test stripthat hosts the reaction only has a limited amount of reagent and canaccommodate only a limited amount of blood. As a result, thereagent-based analysis technique only observes one reaction per teststrip, which corresponds to a single measurement. In order to make asecond measurement to improve the accuracy of the reagent-basedtechnique, a second test strip must be prepared, which requires a secondwithdrawal of blood from the patient. By contrast, the whole-bloodsystems described herein optically observe the response of a sample toincident radiation. This observation can be performed multiple times foreach blood sample withdrawn from the patient.

In the whole-blood systems discussed herein, the optical measurement ofanalytes can be integrated over multiple measurements, enabling a moreaccurate estimation of the analyte concentration. FIG. 30 shows RMSError, in mg/dL on the y-axis versus measurement time on the x-axis.Although measurement time is shown on the x-axis, more measurement timerepresents more measurements taken. FIG. 30 shows an RMS error graph forthree different samples as more measurements are taken. A line is shownrepresenting each of the following samples: a phantom, i.e., a samplehaving known analyte concentration; a combination of glucose and water;and a human sample. Each of the lines on the graph of FIG. 30 show atrend of increased accuracy (or decreased error) as more measurementsare made (corresponding to more measurement time).

In addition to offering increased accuracy, the whole-blood systemsdisclosed herein also have lower manufacturing costs. For example, thesample elements used in the whole-blood systems can be made with lowermanufacturing cost. Unlike systems requiring reagents, the sampleelements of the whole-blood systems disclosed herein are not subject torestrictive shelf-life limitations. Also, unlike reagent based systems,the sample elements need not be packaged to prevent hydration ofreagents. Many other costly quality assurance measures which aredesigned to preserve the viability of the reagents are not needed. Inshort, the components of the whole-blood systems disclosed herein areeasier to make and can be made at a lower cost than reagent-basedcomponents.

The whole-blood systems are also more convenient to use because theyalso are capable of a relatively rapid analyte detection. As a result,the user is not required to wait for long periods for results. Thewhole-blood systems' accuracy can be tailored to the user's needs orcircumstances to add further convenience. In one embodiment, awhole-blood system computes and displays a running estimate of theaccuracy of the reported analyte concentration value based on the numberof measurements made (and integration of those measurements). In oneembodiment, the user can terminate the measurement when the userconcludes that the accuracy is sufficient. In one embodiment, thewhole-blood system can measure and apply a “confidence” level to theanalyte concentration measurement. The confidence reading may be in theform of a percentage, a plus or minus series, or any other appropriatemeasurement increasing as more measurements are taken. In oneembodiment, the whole-blood system is configured to determine whethermore measurements should be taken to improve the accuracy and to notifythe user of the estimated necessary measurement time automatically.Also, as mentioned above, the accuracy of the whole-blood systems can beimproved without multiple withdrawals of samples from the user.

The cost of the sample element described above is low at least becausereagents are not used. The cost to the user for each use is furtherreduced in certain embodiments by incorporating a sample extractor,which eliminates the need for a separate sample extractor. Anotheradvantage of the sample elements discussed above is that the opening ofthe sample supply passage that draws the sample into the sample elementcan be pre-located at the site of the wound created by the sampleextractor. Thus, the action of moving the sample element to position thesample supply passage over the wound is eliminated. Further costreduction of the sample elements described above can be achieved byemploying optical calibration of the sample cell wall(s).

As described above, the measurement performed by the whole-blood systemsdescribed herein is made quickly because there is no need for chemicalreactions to take place. More accurate results can be achieved if theuser or whole-blood system simply allow more integration time during themeasurement. Instrument cost and size can be lowered by incorporating anelectronically tunable filter. The whole-blood systems can functionproperly with a very small amount of blood making measurement at lowerperfused sites, such as the forearm, possible.

In one embodiment, a reagentless whole-blood system is configured tooperate automatically. In this embodiment, any of the whole-bloodsystems disclosed herein, e.g., the whole-blood system 200 of FIG. 13,are configured as an automatic reagentless whole-blood system. Theautomatic system could be deployed near a patient, as is the case in anear-patient testing system. In this embodiment, the automatic systemwould have a source 220, an optical detector 250, a sample extractor280, a sample cell 254, and a signal processor 260, as described inconnection with FIG. 13. The automatic testing system, in oneembodiment, is configured to operate with minimal intervention from theuser or patient. For example, in one embodiment, the user or patientmerely inserts the sample cell 254 into the automatic testing system andinitiates the test. The automatic testing system is configured to form aslice, to receive a sample from the slice, to generate the radiation, todetect the radiation, and to process the signal without any interventionfrom the patient. In another embodiment, there is no intervention fromthe user. One way that this may be achieved is by providing a sampleelement handler, as discussed above in connection with FIG. 22, whereinsample elements can be automatically advanced into the optical path ofthe radiation from the source 220. In another embodiment, thewhole-blood system is configured to provide intermittent or continuousmonitoring without intervention of the user or patient.

As will be appreciated by those of ordinary skill in the art,conventional reagent-based analyte detection systems react an amount ofanalyte (e.g., glucose) with a volume of body fluid (e.g., blood) with areagent (e.g., the enzyme glucose oxidase) and measure a current (i.e.,electron flow) produced by the reaction. Generating a current largeenough to overcome noise in the electronic measurement circuitryrequires a substantial amount of the analyte under consideration andthus establishes a minimum volume that can be measured. One skilled inthe art will recognize that in such systems the signal to noise ratiodecreases with decreasing sample volume because the current produced bythe reaction decreases while the electronic noise level remainsconstant. Modern electronic circuits are approaching the theoretical(i.e., quantum) minimum noise limit. Thus, present state of the artsystems requiring about 0.5 μL of blood represent the lower volume limitof this technology.

Spectroscopic measurement not requiring a reagent, as taught herein,relies on (1) absorption of electromagnetic energy by analyte moleculesin the sample and (2) the ability of the measurement system to measurethe absorption by these molecules. The volume of the sample required formeasurement is substantially determined by the physical size of theoptical components, most importantly the detector 250. In oneembodiment, the detector 250 is about 2 mm in diameter, and thus thechamber 1534 can also be approximately 2 mm in diameter. Thesedimensions can result in a sample volume as low as about 0.3 The size ofthe detector 250 establishes a minimum sample volume because the entireelectromagnetic signal incident on the detector 250 must be modulated bythe sample's absorption. On the other hand, the size of the radiationsource 220 is not a limiting factor so long as the intensity(W/cm.sup.2) distribution of the optical beam delivered by the source220 is substantially uniform within essentially the entire area of thesample and the detector 250.

In another embodiment, wherein a smaller 1-mm diameter detector (such asthe detectors manufactured by DIAS GmbH) may be employed, an accordinglysmaller sample volume can be accommodated. Detector sizes allowingsample volumes of about 0.1 μL or smaller are commercially availablefrom manufacturers such as DIAS, InfraTec, Eltec and others. Oneadvantageous feature of reagentless, optical/spectroscopic measurementis that as the detector size is decreased, the intrinsic detector noiselevel is decreased, as well. Thus, in an optical/spectroscopicmeasurement system the signal to noise ratio remains relatively constantas the volume of sample is reduced. This facilitates the use of smallerdetectors and accordingly smaller sample volumes, which is not the casein the above-discussed reagent-based systems.

What is claimed is:
 1. An apparatus for determining the level of ananalyte in a biological fluid sample from a patient, the apparatuscomprising: an analyte detection system configured to determine thelevel of at least one analyte in the biological fluid sample; a sampleextractor configured to withdraw the biological fluid sample through theskin of the patient; and a disposable sample element configured to beused more than once before being discarded, the disposable sampleelement comprising: a sample cell; a sample supply passage in fluidcommunication with the sample cell; and a container configured to storediscarded biohazardous material; wherein the sample cell is configuredto: receive at least a portion of the first component of the biologicalfluid sample through the sample supply passage; and hold the portion ofthe first component of the biological fluid sample between a firstsample cell wall and a second sample cell wall of the sample cell whilethe analyte detection system analyzes the portion of the first componentof the biological fluid sample to determine the level of the at leastone analyte in the biological fluid sample.
 2. The apparatus of claim 1,wherein the apparatus comprises a fluid separator configured to separatea first component of the biological fluid sample from other componentsthereof.
 3. The apparatus of claim 1, wherein the sample cell comprisesa reagentless sample cell.
 4. The apparatus of claim 1, furthercomprising a blood acquisition system configured to draw the biologicalfluid sample from the patient, wherein the sample supply passage isconfigured to conduct the biological fluid sample into the sample cell.